A Simple Modification Might Have Turned My Perfectly Reliable Toyota Into A Brick. Again

In December 2023, my wife made the wise decision to stop trying to drive a 22-year-old BMW 40,000 miles a year, and instead bought a Toyota for that task. She chose a 2012 Scion iQ for its combination of cutesy weirdness and Toyota reliability. We have driven this car more than 56,000 miles since then, and some bizarre issues have cropped up. The most annoying among them is the fact that the car keeps bricking itself (possibly not its fault — possibly because of a modification), and nobody seems to have a concrete explanation for why.

One of the perks of working from home is that I don’t need to have a “daily driver.” I basically never drive anywhere unless it’s for fun, for an appointment, or to visit friends and family. Because of this, I probably drive my own vehicles no more than maybe 5,000 miles a year, and the vast majority of those miles are put onto something like a single motorcycle for fun weekend rides. Thus, I own basically nothing but cars that were either known for unreliability or would be impractical for a road warrior. People are always surprised when they find that I don’t own a single “normal” car, but that’s the catch: I never have to depend on my cars for anything too serious! If one of my cars breaks down on the road, I can also bodge them back together enough to get back home.

It’s the exact opposite for Sheryl. She is in her car six to seven days a week, and may drive anywhere between 30,000 miles to 40,000 miles annually. Realistically, she doesn’t really have the luxury of having her car broken for more than a couple of days at the most. She can’t really own a car with super rare parts or really finicky build quality. My cars are decent vehicles to drive in the case of an emergency, but I cannot guarantee that my Volkswagens, BMWs, or Smarts won’t try to do something stupid while she’s in downstate Illinois. She also doesn’t have my ability to fix a broken car just enough to limp to a destination.

The Scion iQ was supposed to be the best of all worlds. It’s a weird car like my Smarts, but with Toyota reliability! I have seen lots of iQs with more than 250,000 miles on them, too, so I know they’re good for the long haul.

Love At First Drive

Things were great at first. The iQ had all of 67,000 miles on it when we picked it up, and it was a tight car. The steering was sharp and precise, and it went down the highway surprisingly well for a city car. My favorite part was how the iQ needs basically no space at all to perform a U-turn. The stereo was also a big highlight, and reflected Scion’s old attempts to attract younger buyers with bold colors and loud speakers. Sheryl said that she scored 40 mpg without even trying.

Look, I’m such a huge fan of Smart that I used to own six Fortwos, and even I have to admit that Toyota built a better car than a Smart. Unfortunately for Toyota, building a better car didn’t result in better sales.

Perhaps the biggest test of Sheryl’s iQ was when, in early 2024, we drove the car basically across America along the old path of Route 66. That little car felt like it had conquered America, the Rockies, and all, even though it was really built to rule the confines of New York City or Chicago. We’ve driven this car as far west as the Grand Canyon and as far east as Asheville, North Carolina. The car’s Carfax suggests that, in the hands of previous owners, it’s been even further east.

The iQ has also survived one heck of a beating in our fleet. The car has taken on a full truck tire “gator,” been involved in two minor crashes, and, of course, about 56,000 miles of hard driving. Thankfully, Sheryl’s driving has reduced to about 30,000 miles a year, but that’s still a lot, especially for a car that was never designed to race down the American autobahn. Yet, the iQ has taken the hits in stride, mostly.

After our Route 66 trip, we identified the worst problems with the iQ, namely, the car’s seats, which had about the same long-term comfort as transit bus seats, and the cruise control, or, specifically, the lack of it. Since the iQ has a wee 1.3-liter four with 94 HP on tap and a CVT, you’re usually giving the pedal some push to keep it at typically American highway speeds. That gets tiring on a super long road trip, as the iQ doesn’t have cruise control.

Thankfully, the aftermarket has long solved this problem, and we had a cruise control installed. At least in the Scion iQ, there’s a plug-and-play harness, but also wiring that needs to be tapped into an existing harness. The cruise control cost $800, of which $315 was for the unit.

The Car Bricked Itself A Year Ago

Sheryl then drove 15,000 to 20,000 miles before an insane failure happened. From my previous post:

Every once in a while, the car randomly went into limp mode after misfiring. The check engine light flashed, the car lost power, and slowed down to a crawl. Thankfully, restarting the vehicle restored all functions. The issue didn’t happen again until October. Then, out of nowhere, the issue came back and it appeared both frequently and seemingly entirely at random.

I pulled the codes and found myself baffled. The vehicle recorded a misfire on every cylinder but also a P2121 “Throttle/Pedal Position Sensor/Switch Circuit Range/Performance” code. The vehicle has fresh, name-brand plugs and excellent compression on every cylinder. I couldn’t find any obvious reason for a supposed total engine misfire. Even the car’s battery tested healthy. Eventually, the reported misfires disappeared, so I’m not entirely sure what’s going on there.

What didn’t disappear was the flashing check engine light and limp mode condition. It seemed as if at least once a week Sheryl would report the car going into limp mode with the P2121 code being thrown during the event. Then, this hit a fever pitch. One day, Sheryl left a southern Illinois courthouse to find someone actively slashing her tires. She scared off the guy before the tool went through the tire. But then something truly confusing happened during her five-hour drive home that made us think the vandal did something else. A few minutes after she entered the highway, the engine’s revs shot to redline. She didn’t change her pressure on the pedal. Instead, it seemed the car was trying to accelerate entirely on its own. Thankfully, the car entered into a safe mode where it wouldn’t travel faster than about 10 mph while the engine was seemingly running away.

Eventually, Sheryl was able to limp the car off the highway at 10 mph while the engine redlined. She let the car sit for 30 minutes, and then the vehicle allowed her to drive the five hours or so home without incident.

Once the car got home, I was able to replicate her issue, and it was shocking. A light would turn green, I would hit the gas, and the engine would bang off the rev limiter, but without any movement from the car. Or, alternatively, I’d hit the gas and nothing would happen. The car just sat as if I didn’t have the pedal welded to the floor. If I were lucky, the car merely went into limp mode and I had a top speed of 45 mph. Sometimes, the car could be cruising at 60 mph, and suddenly, the pedal would stop working.

I had a theory as to what happened here. About once a month or so, a Smart owner comes into a forum or group and complains that their gas pedal mysteriously no longer works. Back in my IT days, I learned that a great way to troubleshoot is to uninstall modifications first, and then start with a stock system. So, that was the advice I gave those people. I noticed that nearly all of the people who had pedal issues in their Smarts also had aftermarket cruise control systems. I’d have them disconnect their cruise controls, and in an instant, their gas pedals began working again.

As it turned out, some aftermarket cruise controls in Smarts have substandard soldering, and when the soldering goes, the gas pedal gets bad signals. This is because the cruise control routes directly through the digital pedal, so bad signals coming from the cruise control go into the pedal.

It sounds like there might be a similar issue that can happen with aftermarket cruise controls in Toyotas, too. At any rate, the cruise control had a warranty, so Sheryl had the dealer investigate. Here’s what was found:

A couple of techs at the local Toyota dealer worked through the weekend to replicate and troubleshoot the problem. The limp mode issue never showed up for them.

However, the tech who installed the cruise control found a bunch of fault codes stored in the cruise control unit itself plus that persistent P2121 from the car. Their diagnosis? The cruise control is having a failure of some kind, which sends bad signals to the accelerator pedal sensor. As for the P2121, it was found that the pedal sensor was also failing. The consensus is that the cruise control failure damaged the accelerator pedal sensor.

Unfortunately, the cruise control warranty covered only the unit itself. Since Toyota does not sell the accelerator pedal sensor itself, you have to replace the entire gas pedal. We ended up paying out of pocket to replace the pedal. It stung, but Sheryl got her car back with a shiny new pedal that actually worked better than the car’s original one.

The dealership then had us drive the car for a month with the cruise control disconnected to see if anything happened. The car drove just great, so the dealer decided to replace the bad cruise control with a new one. Finally, I thought, it was all over.

Here We Go Again

That was back in December 2024. It is now October, roughly 10 months and about 25,000 miles or so later. Sheryl has been telling me that her car is broken again. This time, the car has new and exciting issues for us.

The first is that our old friend P2122 came back. This time, the error manifests itself in a weird way. In most instances, we hit the gas and nothing happens. But as a twist, restarting the car doesn’t fix it, and hitting the gas after a restart results in the same non-movement. Sometimes, we have to restart the car two or three times before the pedal begins working again.

The other issue is that, at least once a day, as soon as I hit the gas, the engine sputters, stalls, and shuts down. Restarting the car sometimes results in it immediately sputtering and shutting down again. This issue is always accompanied by the pedal not working. If the pedal is working, the car isn’t stalling. Annoyingly, the car is not producing any engine codes when this happens. I don’t even find any “secret” codes with my fancy Autel scanner. Just the frustrating P2122.

There are two more issues, too. The CVT emits a concerning whine, and, when idle, I can feel a slight miss in the engine. Some of this is explainable. The car has 123,000 miles now, and according to the service records I could find, the car has its original spark plugs. I bet the slight miss will be solved with a spark plug change. That should also fix the problem we’ve been having with the car scoring only 23 mpg recently.

The rest of the issues are leaving me scratching my head. This time around, the dealership is unsure if the cruise control is a cause of the issue or just a symptom of it. At any rate, their solution is to just replace the pedal and the cruise control again. I don’t like this resolution, because that’s what didn’t work last time, and there’s no guarantee it’ll work this time. The pedal is a $200 part, and it’s insane that we’ve now lost two pedals in the span of just 10 months.

But I’m not really sure what to do about this. I’m not entirely sure how to troubleshoot this outside of just deleting the cruise control entirely, replacing the pedal again, and hoping we don’t end up right back here 10 months from now. But Sheryl loves the cruise control, and will hate staring at a dead cruise control stick, knowing she spent $800 on a pile of crap that she can’t use.

I feel like there are three possibilities here. Either the new cruise control encountered an error and killed the pedal again, or the pedal is dying because of some other issue with the car, or there’s some issue within the pedal part itself. Worse, since it takes 20,000 or more miles for the pedal to die, replicating it isn’t easy.

Solutions?

At the very least, I have a temporary solution. There’s no way around it; the current pedal is trash. So I’ll buy another one. Only two bolts hold it on, so I’ll install it myself. This time, instead of having the dealer replace the cruise, we’ll just disconnect it. We also called up an independent Toyota mechanic just to get a second opinion on what’s going on here.

Replacing the spark plugs is a bigger job than it should be. To get to the spark plugs, you have to remove the windshield wipers, the cowling, the airbox, and move around the rubber hoses. It’s a royal pain, and that’s due to the really tight packaging in the engine bay. I’m thinking about replacing the ignition coil packs while I’m in there.

Normally, I would not touch coil packs unless I know they are having issues. However, there are three things on my mind. The first is that these packs have 123,000 miles on them already, and Sheryl beats the crap out of this car. The second is that, if I replace the plugs, button the car back up, and find out the coils are bad, I’m not going to be happy to have to tear it back down again. The third is that, as I stated earlier, Sheryl doesn’t have the luxury of downtime. The car can’t be broken while I’m futzing around with coils and diagnosing issues. So, I’m feeling like I’ll just throw a fresh set of OEM coils in there as peace of mind. In the worst case, the original coils can be spares.

I’m hoping that, between the new plugs, coils, gas pedal, and disconnected cruise, the car will stop bricking itself and go back to being the reliable Toyota that it used to be.

Sadly, I’m not entirely sure what to do about the CVT aside from changing the fluid again. We changed the CVT fluid at 80,000 miles. The transmission has been whisper-quiet until about 5,000 miles ago. Now it’s loud again, just like it was during our Route 66 trip. The dealer says that the transmission will “either whine for the next 150,000 miles or blow up next week.”

At the very least, I have been able to confirm that there are plenty of complaints online about dying gas pedals and CVT whine in Scion and Toyota iQs. That bit is fascinating, but also reassuring. It’s good to know that it’s not just us experiencing these bizarre issues. I suppose it’s also sort of sad. You’d think that drive-by-wire would be so reliable that the idea of pressing the gas and nothing happening would be nearly impossible. Yet, here we are.

Anyway, here’s where I turn things over to you. Am I on the right track here? Am I missing something? Is this darn car haunted? Hopefully, the next time I write an update about this car, it will be a bit happier.