Analysis: The IS500 Bumper Cover Separation Issue

Editor’s Note:

• This article has been updated in August 2024 with new developing information.
• As a prerequisite, it requires a small amount of automobile knowledge to fully comprehend this analysis.

The IS500 is a low-volume model in the Lexus IS product line, with around 1,000 units built and sold in the US market for the 2022 model year. However, within the IS500 fans circle, we have already seen two common issues. One is the Check Engine Light problem, and another is the front bumper cover self-separation issue, which this article is going to cover.

First, let me show you what is the front bumper cover separation issue. Lexus had one red IS500 on display in the 2022 OC Auto Show this past weekend, and that demo car has the same symptom, see the below photo: pay attention to the front bumper cover where it meets the headlight and the fender, the gap is widening and the cover seems to be partially separated from the fender.

This issue only happens on the driver-side, the same as what happened to the majority of owners who were reporting this issue. Some owners have let Lexus dealerships attempt fixing it, but the same symptom came back after some time.

As of August 2024, the latest developments on this issue are as follows:

1. Toyota issued a TSB claiming to resolve the issue. However, many owners on Lexus forums have reported that the TSB not only failed to fix the problem but also accelerated its occurrence or made it worse.
2. In response, a forum member developed a homemade kit (which has gained popularity and high expectations among IS500 owners) designed to reinforce the retainer tab, hoping it would create a firmer connection with the clip and prevent them from coming apart. Unfortunately, as analyzed later in this article, this solution is at best a temporary fix and is likely to fail over time. Here’s what one owner has reported:

From my point of view, the root cause of this separation issue is very concerning. Let me state my conclusion first, and I will show some data and examples, provide my analysis and reasoning to illustrate why I believe this is the only possible explanation. Please note this is my opinion only and it is all up to the reader’s judgement whether there is any better theory that can explain all of the observed symptoms. I welcome any new theory or explanation if they can better dissect this issue. In fact the best way to prove I am wrong is: find a way to permanently resolve this issue without altering the design (punching a hole in the bumper and riveting it to the body frame does not count). So far, no such solution exists.

With the latest information available as of August 2024, my latest conclusion on the root cause is:

Note: as already mentioned previously, the IS500 is not the only model/trim that experiences this issue, a couple months ago I already listed several reported cases that some 2014+ IS (non IS500 trims) also had this similar issue. Recently, quite some of the 2021+ IS350 owners started to report the bumper separation issue, for example see here. This does NOT contradict with the above conclusion: the heavier the engine is, the sooner the car will experience this symptom. And this does not preclude the smaller engine models – they just shows up later and at a slower pace than the IS500.

This is a long analytical article, if you want a quick and convincing answer, simple take a look at the below example of the last generation Subaru BRZ/Scion FRS/Toyota 86, then you should be able to understand the IS500 case (the IS350 will be similar).

The 2013 – 2020 Subaru BRZ/Scion FRS/Toyota 86 front apron separation issue: it is a well-known symptom in the last-gen Subaru BRZ/Scion FRS/Toyota 86 that, there are overwhelming customer complaints on the driver side front bumper cover separation. Subaru finally admitted the issue and released a technical service bulletin explaining the cause and showing how to fix it. Basically speaking, Subaru confirmed that the issue is caused by “the claw of the front bumper rubs against the bracket corner and damages it” (see below the 2nd image for illustration of the damage location). Obviously the only possibility that generating this rubbing effect is body flex. Specifically speaking, it is the front section (engine compartment) of the vehicle exhibits body flex to the extent that the induced rubbing force is large enough to damage the holding clip. You can download the service bulletin here, but I will post the first 2 pages here to show how and where the clips were broken.

One thing worth to point out: the fix by Subaru actually does not work – look at the #85 reply in this thread, after applying the TSB, the damaged clip (the previous culprit) is strengthened by the metal plate, but now it is the claw’s turn to be ripped off. So the symptom resurfaces again (according to the owner in the thread, the fix held up for one day only). Therefore unless the root cause (body flex) is completely addressed, there is no permanent solution to this issue.

There are empirical evidence indicating the IS500 bumper sagging issue, from appearance to the root cause are all exactly the same as the Subaru BRZ/Toyota 86. Body flex is the only possible cause that I can think of.

Before proceeding to more technical discussion, let me clarify four common misunderstandings among the affected IS500 owners.

Rumor 1: the IS500 front bumper cover sagging is due to its slightly longer (and heavier) than the standard IS.

Fact: this is impossible because the IS500 front apron is only about 2 inches longer, and the added weight is negligible. Moreover, if weight were the issue, the sagging would occur on both sides, as the bumper cover is completely symmetrical. The driver’s side is neither heavier nor differently shaped. However, what we’ve observed is that the sagging occurs only on the driver’s side.

Rumor 2: there is a manufacturing defect in the bumper cover’s driver side clip, so the symptom only happens on that side.

Fact: Firstly, there is no direct proof that there is a manufacturing defect in the IS500 bumper cover; if someone suspects the driver side clips look different, or are thinner or weaker (in fact when the owner was examining the clip, which the sagging had already happened, he was looking at the clip that had been damaged/ripped by the claw like the Subaru case, which made it look like to be different), refer to the above Subaru BRZ case: after reinforcing it using metal plates, see what is the final result? Still failed. Secondly, IS500 is not the only model/trim that experiences this issue. In fact, it is a common issue in the 2nd-gen IS with “shorter” bumper cover (see this post, and also this post), and the current generation IS as well (non IS-500 trims are also affected, see this post, this post and this post): driver side bumper cover sagging. There are abundant additional examples if you do more research on the internet (for example the Subaru BRZ/Toyota FT86 above; also the STI, the Ford Fiesta, and many more). The theory of driver side clip defect means multiple mainstream automakers like Toyota, Subaru, Ford etc. intentionally made defected front bumper covers over a couple decades and across multiple models, and those defects all happened to be in the very same driver side clip. What are the odds about this? Is it even practically possible?

Updated 09/2023 – Rumor 3: the summer heat cause the bumper cover plastic becomes soft, which cause the sagging.

Fact: Examining the timing of the reported cases shows that they are evenly distributed throughout the year. The separation occurs once the retainer clip has worn to the point where it can no longer hold, which depends on factors such as driving style, mileage, road conditions, and how these factors accumulate over time. While some may notice this issue during hot summer days, there have been reports of it occurring in colder months as well. Geographically, affected owners are not limited to warmer climates – cases have also been reported in colder northern states like New York and North Carolina. Additionally, it’s important to note that statistics may not always indicate causation.

Updated 10/2023 – Rumor 4: Lexus claimed the 2021+ facelifted IS chassis is stiffer than the pre-2021 models, so there cannot be body flex.

Fact: car body stiffness is a very broad and ambiguous term. It has many different definitions and it can mean anything. For example there are static stiffness and dynamic stiffness; and it can also mean global stiffness, or local stiffness (each section of the car body has its own local rigidity). A vehicle can have stronger dynamic stiffness but weaker static stiffness coexist at the same time; Similarly, a vehicle has stronger stiffness at some local sections, may not mean it has stronger global stiffness. If you look carefully at Lexus’s official press release, it tells you where they enhanced the stiffness: “reinforcing the radiator side supports, increasing the number of front-side-member weld points, and optimizing reinforcement structures from the C-pillars to the sides of the roof“, the changes are at the passenger cabin, NOT the engine bay and front bulkhead. The use of mild steel will of course weaken the local stiffness – if downgrading to mild steel can keep or improve the stiffness, then why in the 2021+ facelift, they still bother to change part of the cabin section from mild steel to HSS, and then claimed the cabin structure is optimized and reinforced?

Only a structural issue, such as body flex, can reasonably explain this problem. Anything related to structural rigidity is not easily fixed. It’s clear that all model years of the IS500 suffer from this issue, and no effective solution has been found so far. This is evident from the fact that IS500 models from various years continue to experience the problem. For example:

You can see more owner reported cases in those Facebook groups (search by keywords like “IS500” to find those groups). What we have observed are:

1. The issue occurred on all model years so far (2022, 2023 and 2024);
2. In some cases, the owner noticed the happening of the issue immediately after taking a spirited drive or participating some sort of racing event;
3. After repairing (either by pushing it back to place, or replacing the clips or even the whole bumper cover, or the official TSB, or even the Etsy kit), the same issue still came back again.

Now, let’s dive into a detailed analysis by reviewing some background context.

No material in the universe is absolutely rigid, including metal, meaning that every car’s body will flex under stress. The key difference lies in the extent of that flex. Higher rigidity results in less flex and makes permanent deformation less likely, while lower rigidity leads to more flex and a greater risk of lasting damage. Body flex is a natural occurrence and isn’t necessarily a bad thing. What we want to avoid is excessive flexing, which can tear components apart and cause permanent deformation.

A bumper cover, being made of soft plastic, is naturally capable of withstanding a certain degree of flex without detaching from the car body. However, there is an upper limit to this flexibility, and once that limit is exceeded, visible issues begin to emerge.

Concern for all the 3rd-gen IS

The Lexus IS has relatively weak rigidity in several aspects, due to the facts listed in this structural analysis article:

• The 2021 facelift downgraded the front rails material to mild steel (not the HSS used in the 2014-2020 models) – this is the major and common reason that why ALL 2021+ IS will potentially have the bumper cover separation issue.
• According to IIHS test data (click the link above to review the actual data), the 2002 Toyota Camry- a 20-year-old model – performs better in the moderate overlap frontal crash test than the latest Lexus IS. When considering impact rigidity from all three directions (front, side, and roof), the 2007 Toyota Camry is on par with or even superior to the latest Lexus IS. It’s important to note that while IIHS has introduced several new tests in recent years, the testing methods and standards for the moderate overlap, side impact, and roof strength tests have remained consistent.

The above factors indicates, not only the IS500, but also other trims (IS350, IS300 etc.) may experience the same bumper cover separation issue as well.

How come a luxury brand model came out in 2014 and refreshed in 2021, is structurally weaker in taking impact stress than the non-luxury low cost model which is 10+ years or even 20 years older? What is the explanation to this observation?

Although crash test measurements do not 100% equivalent to torsional/bending rigidity, they are correlated. For example cars with high torsional/bending rigidity typically perform very well in crash tests and vice versa. With that being said, it is clear that Lexus design philosophy is somewhat different than other auto makers: the luxury brand/higher-end models may NOT be more rigid in crash test than its budget brand’s lower-end cars. It appears to be they may want to recoup the higher per-unit development/manufacturing cost due to lower sales volume (Toyota sells less IS than the Camry), by saving costs in areas that a “normal” consumer cannot easily see or feel.

From information in the above mentioned article, we can conclude both of the IS passenger cabin, and the rear bulkhead have higher local torsional rigidity than the front structure, therefore most of the torsional stress applied to the car body will ultimately find their way to the front structure to be released (through body flexing). Compounding the fact that front rails now are downgraded to mild steel, this makes the structural flexing symptom to be excessive.

Issue specific for the IS500

During the auto show, I grabbed the IS500’s bumper cover, lifted it and tried to push it back. It takes a large amount of force to make the bumper cover move up enough to fill the gap to look like normal. However it will not hold up there at all – once I let go of my hand, it immediately dropped back. This is understandable: for that amount of force needed, it is something not a couple of clips between the fender and the bumper cover can handle.

When this car is being assembled in the factory, if it requires such force to snap the bumper cover into the fender during that time, the clips will break immediately due to this built-in stress. Since this is not the case, it means: (1). the clip is damaged (like the Subaru case above); and (2). the geometry of that area of the IS500 has been altered. Specifically speaking, there may be a slight permanent frame deformation occurred in the IS500’s front structure. When you are standing in front and facing the vehicle, there is a counter-clockwise “twist” to it: the driver side front rail, strut tower and fender are lifted upward, and the passenger side is down. This will “tear” the driver side fender apart from the bumper cover.

I also find a symptom that indirectly infers this conclusion: for the IS500 on display in the auto show, I find its hood is misaligned to the fender on the driver-side: the fender edge is approx. 1-2mm higher than the hood (see below image, where the grey arrow points at) at the front, while no such issue at the back closed to the windshield, and the passenger side is flush without such a problem as well. This may indicate the driver-side front structure is bent upward, and this situation is more aggravated in the fore-strut area.

Please note that the above description is for that specific IS500 in the OC auto show. Bumper sagging may happen well before the car body permanent flex occurs – as long as the rubbing damage has developed in the clip, sagging will start to show up.

Now it brings us two questions: (1). why this perceivable “twist” happened on the IS500 more prominently? (2). Why this is affecting the driver-side, not the passenger-side?

Let’s look at the first question. The engine is a large, heavy metal object attached to the engine cradle (also called the front sub-frame), which in turn is attached to the left and right front rails of the vehicle. When the vehicle is driving on roads, the unevenness of the road surface will cause the vehicle to vibrate in the left-right direction, and transfer to the engine. Due to inertia, the engine’s vibration will generate a corresponding twisting force in the left-right direction, applying to the vehicle’s left and right front rails as well.

The heavier the engine, the larger the inertia twisting force it generates. From 2022 IS specification, the V8 engine on IS500 is around 121 lbs heavier than the V6 on IS350, or 150 lbs heavier than the I4 turbo on IS300, so there is 120-150 more pounds of weight “shaking” the front rails. Technically speaking the most effective solution is to add a reinforcement brace, for example a strut tower bar in the engine compartment, and this is exactly almost all other sedans/coupes do in their V8 variants (or variants with a significant heavier engine), this is so true that a casual search on the internet will provide you ample of examples:

The key point of reinforcement is, if standing in front and facing the vehicle, the imaginary line that connects the brace attaching point of both sides, should be in front of, or at least near the gravity center of the engine.

Another example is the B5 generation Volkswagen Passat W8. VW managed to put a 8-cylinder engine in the FWD platform (by the way, the B5 platform is using longitudinal engine layout – this and FWD are not mutually exclusive). The entire engine, plus part of the transmission, are placed in front of the front axle. The car is nose-heavy with 60% of the weight in the front, and there is no extra reinforcement to the side rails/fenders. Some of the Passat W8 exhibit the same bumper sagging symptom and like the IS500, the driver side sagging is more prominent. See this example:

Compare to the passenger side, there is no perceivable sagging on the bumper:

let’s take a look at the driver and passenger sides at the same time, you can see the driver side sagging is extended to the headlight area. The driver side has a wider gap between the headlight assembly and the bumper.

Now back to our main subject: there is no evidence in the body structure that can make the IS500 immune to the front chassis flex, without leveraging front structure reinforcements, because even the RC-F needs, and indeed installs the strut reinforcement bar (that connects each strut tower to the firewall) from the factory.

What aggravates the situation is the extremely tight fit of the 90-degree V8 engine inside the IS’s engine bay. Since there will be vibration and shaking when the engine is running, to optimize the cabin NVH, the engine mount usually needs to provide some “cushion” and play between the engine and also the sub-frame’s mounting point. Since the V8 is a tight fit on the IS500, it has to use stiffer engine mounts to limit the play and prevent the engine from hitting the strut towers during operation. Stiffer engine mounts will lead to larger peak stress to the mounting point, which also contributes to a greater twisting force to the front rails.

Of course, stiffer front suspension is another contributing factor to the elevated stress. When the driving mode is at the “normal” setting, the IS500’s suspension is still stiffer than its IS250/200t/300 siblings. As an experienced reviewer and tester, I can feel the slight trembling (structural shaking) originated from the front of the vehicle whenever the IS500 goes over a pothole or uneven concrete joints on the road.

There is another type of factor that generates the twisting force, which also explains the second question: why does only the driver side exhibit this issue?

As stated earlier, when standing in front and facing the vehicle, the twisting force is in the counter-clockwise direction, so this will “tear” the driver side cover apart from the fender, and “compress” it on the passenger side (good to minimize the gap!). The counter-clockwise twist comes from two sources:

1. when you are sitting inside the cabin and look forward, the 2UR-GSE V8’s flywheel is rotating in the counter-clockwise direction, since the load from the transmission’s torque converter is trying to not letting the flywheel to rotate (Newton’s third law of motion), this generates an upward force/torque to the driver side engine mount (and a downward force to the passenger side mount). Calculating from IS500’s output spec and the transmission ratio, when in 1st gear, there will be 5,688 lb-ft of twisting torque applied to the engine mounts, which is much higher than when equipped with the V6 (4,032 lb-ft) or I4 turbo engine (3,715 lb-ft).
2. In the North American market, the driver sits on the left-hand side. For IS500 it is arguably the most frequent use case that the driver is the only person in the car, so the driver side of the car is heavier than the passenger side. This means the driver-side strut tower always receives the bigger road force impact stress, which translates to a bigger upward force applied to that side’s subframe/front rail as well.

As a supporting example of the above #2 factor, more internet search reveals that not just the IS500, many other cars, like the Subaru BRZ/Toytoa 86, the Impreza etc., all have the bumper cover sagging issue happen on the driver side.

During the design phase of a car model, engineers will estimate and calculate the load and stress that the car frame needs to endure and provide sufficient torsional and bending rigidity to suppress it. For a heavier V8 engine with higher torque, a beefy front structure is needed to handle the extra weight and twisting torque. However, from the above listed data, the current IS lacks this.

Do not underestimate the impact of the heavier engine and larger torque to the car body structure, it definitely is not exaggerated and this requires an extra strengthened structure to handle. Let’s take the 2021+ Acura TLX as example. For the Type S variants, they are using a V6 turbo engine while other trims are using a I4 turbo engine. The V6 is heavier with higher output (355 hp v.s 272 hp, and 354 lb-ft v.s 280 lb-ft of torque). The output difference on the TLX case is way smaller than the difference between the IS500 and other trims. However even with those smaller output difference, Acura already needs to reinforce multiple load bearing structural parts for the already-very-rigid TLX body. Please note the SH-AWD is not the reason here because that option is also available on the less-powerful 2.0T trims, which does not have the Type S structural enhancement.

See below illustration, to handle a heavier engine, and the extra 83 hp and 74 lb-ft of torque, Acura changes:

• increased the thickness of the steel sheets which form the front rails, from 1mm to 2.3mm;
• added extra bracing to the strut towers and rear bulkhead ring;
• added extra reinforcement/patch to the mid floor cross member.

Now look back at the IS500, you will not see any changes to its structural components.

Not using HSS for the front rails is a bad decision as well. Let’s put it this way: if using mild steel is sufficient, then Lexus would have done the same thing for other higher-end models such as the GS, RC etc. given they have similar curb weight. But this did not happen. Why?

Below illustrations show the materials for various Lexus models, only the IS is using mild steel for the front rails.

With that being said, when and how serious this front bumper cover separation issue happens depends on: (1) how the IS500 is driven and (2). the owner’s local load road conditions. If you make use of the V8 torque more frequently (not necessarily driving fast – when you accelerate from a traffic light or pass another vehicle on the highway, the V8 has already output lots of torque), do more aggressive cornering, or your local roads have potholes or uneven expansion joints, then the IS500 may develop this issue sooner, and the widening gap is more noticeable. The red IS500 in the auto show has been used as a media loaner. From the wear of its tires, I can see this IS500 has been driven aggressively (typical treatment when the media tests data such as 0-60, 1/4 mile, road holding/skid pad, track lap time, etc.), which brings higher stress to the car frame, so no wonder we see the separation issue.

Based on the above analysis, the only possible solutions are:

1. Redesign the front structure and make it more stiff and rigid; or:
2. Change the material of the front bumper cover to make it more soft and flexible, so that even if the fender is moved, the bumper cover can still follow the flex and keep attaching to it.
3. Reinforced the clip to “force” the bumper to stay fit with the fender, for example as mentioned in the above Subaru service bulletin, the below metal plate may help to fix and reinforce the damaged clip:

Only the #1 will be the fundamental permanent cure, other approaches are essentially stopgap only – the stressed generated from body flex and rubbing still need to find place to go and be released. For example as mentioned at the beginning of this article, some Subaru BRZ owners reported even after performing the above service bulletin fix and adding the metal plates, the bumper sagging still reappeared after a certain time period.

For the Subaru BRZ it took the auto maker 6 years to admit the issue and provide a substantial solution; for Toyota, although it is the same car and the evidence and solution are so obvious, now 10 years has passed, they never admitted anything or took action. Therefore, for the IS500, given its sales volume and remaining life span, I have my reservations on whether Toyota/Lexus will take this seriously. On another note, owners of the IS500 should feel fortunate that the vehicle releases the flex stress at the bumper cover attachment, while the Tesla Model X owners are not so lucky that the EV chose to release the body flex stress from the cabin load structure and the welding is teared apart. Anyway, let’s keep our fingers crossed.