Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Toyota Tacoma Engine Light

I recently bought a 2001 toyota Tacoma from a chevrolet dealership and the night I bought it the engine light came on. i took it back the next day and they scanned the computer code and told me the oxygen sensor needed to be replaced. since they had replaced the catalytic converter at a nearby toyota dealership under warranty before i bought the car, they would find out if the oxygen sensor was under warranty and if not they would replace it themselves- which they did. the next day the engine light came on again so it took it back and they said the other oxygen sensor needed to be repalced which they did. the next day the engine light came on again and i called them and they told me they had no idea what was wrong and they set up an appointment at the nearby toyota dealership who had replaced the catalytic converter. they said the computer was broken and so they replaced it. the next day the engine light came on again and so i called the chevrolet dealer ship who said to take it back to the toyota dealership to diagnose it and after 6 hours they said they had no idea what was wrong with the car but it might be the gasoline. the next day the light came back on again but it went off the next time i re-fueled then came back on again. is this car a lemon or is the check engine light not a big deal? is there something wrong with the truck they should be able to find and fix?

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Joe, your cut-paste answer does not answer her questions even remotely in this case.

Check engine light is a huge deal in a state where you have emissions testing since it will never pass. It also means potential problems down the road.

Check your state laws on this, in MA you would be able to return the truck for a full refund. The CEL light that just went on stored a code that can be read as Joe described. Don’t do this yourself but let the Chevy dealer or Toyota do this.

The truck is fixable likely but something is more difficult than usual. I would pose to the dealer that they take care of it or kindly ask for your money back or exchange for something else.

Not sure if you picked because of the “Toyota” name. But they are no or less infallible to problems than any other make. Luckily across ALL makes the majority of vehicles tend to be reliable. Just a smaller subset are not.

Thanks for your replies! Like I said I’ve had the codes scanned 4 times now, twice by the Chevrolet dealer and twice by Toyota- the only service record that has a code is P0420.

Much of this problem has been caused by Toyota Motor Car Company, parts suppliers, and parts catalogers, and, then, ignorance on the part of would-be repairers. Ignorance is curable. The other stuff…I don’t know.
I’m not trying to be factious by saying that the Chevrolet dealer should farm this job out to the Toyota dealership. The Chevrolet dealer has, already, sunk a number of expensive parts into it, haven’t they? Farming it out could, actually, save them money,as compared to throwing more parts at it, right?
At the crux, I think, is the matter of getting the correct part to install. Late model Toyotas, at least some, use what is called (either) a wide-band oxygen sensor, or (the exact same thing) an A/F Sensor (Air/Fuel). The “wide-band” oxygen sensor may be used in the front of the catalytic converter. It may, or may not, be used in the back of the catalytic converter. A regular oxygen sensor (“narrow-band”) may, or, may not, be used there. (See how simple it is?).
To further complicate matters (Thanks, whomever!), the criteria for getting the correct part depends on: 1. Is it a 4 cylinder, or a 6 cylinder? 2. Does it have an automatic transmission, or a manual transmission? 3. Is it an extended cab, or not? 4. Does it have California emissions package, or Federal emissions package? 5. And, of course, is it the front (of catalytic converter) sensor, or the rear (of the catalytic converter) sensor?
Vehicles which use A/F Sensors, use very different parts than those with “regular” oxygen sensors; but, they don’t appear to be that different. The catalytic converters are different, the engine computer, and other stuff are different.
Oh! Not all mechanics, or service people, know this stuff. A shame. You could download, and print, this little note for them.
Here’s a link to a parts supplier. It shows some of the things which can cause this confusion. The two brands, Bosch and Denso, are both reputable brands. It’s just that Denso is about twice the price of Bosch.,16100117/shopping/partTypeResultSet.htm

ADDED: Diagnostic Trouble Code (DTC) P0420, “Catalyst system below threshold (bank 1)”, can be caused by the wrong type of parts (wide-band, or narrow band oxygen sensors), etc.,being in place. In short, it needs troubleshooting by an adequate mechanic,with adequate tools, and adequate knowledge.

Thanks again- this is very helpful information. Question: Since the Chevrolet dealer scanned the computer codes and replaced both oxygen sensors (at their expense), do I go back to them and ask them to straighten this out or since it was the toyota dealer who replaced the catalytic converter and computer (under warranty) do I bring it back to them to straighten it out or should I bring it to another Toyota service center ( wont they want to talk to the other two mechanics who have worked on it so far) or can they fix it by taking a look at the parts that are on the car now and the computer codes?

Take it back as a lemon, or to the dealer you bought it from and that you have the warranties with. Whoever repairs this, or attempts to, can decide to talk to the other dealers, shops, mechanics, if they desire. Maybe you should bail now, as the shops / mechanics who have worked on it so far don’t seem to know what they should know. It’s not your job to educate them.

Thanks, I appreciate it. Luckily the truck had under 40,000mi when I bought it which means I might get a refund even though under Massachusetts Lemon Laws, I stand to lose 50 cents per mile that I have driven the truck since I bought it and since I drive it for work, I’ve got 2000 miles on it already so it’s $1000 gone and the meter is still running but I’ve already made 6 trips and spent 6 days in the shop with it and I dont have any confidence that the dealer I have warranties with can do the job or farm it out to competent people and I dont want to deal with any more problems with it at this point since it sounds like some of the work that was done already was done incorrectly and they’ve had 6 or 7 chances to fix it at two different shops. I didnt want to go back into the market to shop for a vehicle with less money than I had a month ago but it sounds like the car is really a lemon and better to bail than to be stuck with it since it could costl more down the road.

I don’t think the vehicle sucks. All vehicles will have problems. I think the service suc…, er…I mean, is sub-standard.

I understand that all vehicles will have problems but what I don’t understand is that the check engine light goes on and off at random for example it went off the last time I filled up but then it came back on when the tank reached half way and today it went off while I was driving in the rain, and that is what makes me think it is a lemon or has an electrical problem, but my boyfriend thinks it could be the carbon fuel filter.

How about this? I took it to another Toyota dealership for a second opinion and their diagnosis is “Coolant fan clutch coupling not releasing causing coolant temp to stay low, recommend replacing.” She said something about it overheating, which sounds bad. Some notes on the work order are more specific “Coolant temp not reaching 210 degrees” so I am confused since it sounds like the diagnosis is that it is not heating up yet she told me it is overheating. Has anyone ever heard of this problem?

Yes, that is confusing. Who is “she”? The service writer, or whom?
A lot of people are confused about what temperature is “overheating”. They think that any temperature above the temperature that the thermostat opens is overheating (180F to 195F degrees. 'Tain’t so. The normal operating temperature is 220F to 240F degrees. Why? Because the cooling system is pressured to 15 psi. The temperature could rise to 265F degrees before boil-over occurs, if the system is sealing as it should be.
A thermostat sticking open can cause the engine coolant temperature to run too low (below 220F degrees). So can a radiator fan which blows too much or too long.
What has happened to the emissions/engine management problem(s)?

She is the Service Manager. The car is not overheating since the coolant is not overheating because the fan will not shut off- as I read this, she is saying the fan is overheating and setting off the engine light? It makes no sense to me but this is their new answer to the P0420 code. I read something online at that said one possible cause for the check engine light is " The Engine coolant temperature sensor is not working properly." I gave them your suggestions that the Chevrolet dealer used the wrong 02 sensors in the wrong place, and the truck’s current symptom which is that the check engine light goes off when I fill up the tank and it comes back on when it’s half way down- other factors might be rain, just kidding, or bad gas, as the other toyota dealership claims.

P0420 is “catalyst system efficiency below threshold”. This fault code is tripped when the signal from the oxygen sensor downstream of the catalytic converter is insufficiently changed from the signal from the oxygen sensor upstream from the converter.

Any knowledgable shop can put the output signals from the two oxygen sensors (they’re voltage outputs) on a scope (engine analyzer), look at the actual signal traces, and tell what’s going on. The upstream signal shoudl fluctuate, resembling a “noisy” sine wave, and the downstream signal should be more flat with a higher voltage output than the average of the upstream signal. Analysis of the traces could disclose an erroneous signal, a missing signal, or may even disclose that an improper cat converter was used and cannot “cut the mustard”.

Now, to your comment about the CEL going off when you fill the gas tank and going back on when the tank gets to 1/2 full…this may be a seperate problem and be confusing the issue. Your gas tank needs to breath in as the gas is pumped out, and it does this through a canister with an activated charcoal bed located under the hood. If the charcoal bed is saturated or the line is kinked or other wise plugged, when enough gas has been pumped from the tank a vacuum can develop in the airspace and prevent the pump from maintaining proper pressure. This can trip a fault code in a few different ways. When the tank is refilled, the vacuum is broken, the pump pumps fine, and the code resets itself.

You can easily test this. When the tank has run low and the CEL comes on, shut the vehicle off and remove and replace the gas cap. If you hear a loud whoosh and the CEL light goes off, you may need to have your evaporative emissions control system checked out.

Oh, the “bad gas” thing is balogna. That excuse is probably the most common excuse used by incompetents who cannot or willnot do the diagnosis propely.

Thank you- but I am getting discouraged that neither the Chevrolet dealership nor the two Toyota dealerships I’ve brought it to can properly diagnose it or fix it. I’ve tried to get it fixed or diagnosed 5 times so far and once before I bought it, the dealer tried to diagnose and fix the same problem. I have an arbitration hearing at the Massachusetts Attorney General’s office on December 17th that handles Lemon law issues and something will be decided then, hopefully in my favor. BTW, it’s 15 cents a mile and not 50 cents a mile I would stand to lose if I get a refund. I’d be surprised if the catalytic converter they replaced isnt cutting the mustard- that was replaced under Toyota warranty at a Toyota dealership so I assume they were not using aftermarket parts but another friend of mine said he had never heard of a cat converter being replaced on a truck with so few miles.

Further clarification… the shop says that since the coolant fan isnt shutting off it isnt letting the engine get warm enough that’s why its sending a bad signal or reading the O2 sensors or the rear sensor as a noisy sine wave?

I’m not buying that. When the engine is cold the oxygen sensor loop is intentionally bypassed in order to allow the engine to run rich without triggering a code.

Further, a cooling fan not shutting off will not prevent the engine from warming up. When the engine is cold the thermostat will close and the coolant will not be moving through the radiator in sufficient quantities to cool the engine down (there’s a bit of bypass). If the coolant is not going through the radiator, how could the cooling fan affect it?

I still suspect that someone installed either a wrong converter or (as Kit suggested) an incorrect sensor.

And I still suspect that your CEL coming on when your gas tank gets down to 1/2 full is a different and unrelated problem.

I still think the engine needs to go on an analyzer, the sensor traces need to be read, and you should try the “pull the gas cap” trick to see if it affects the CEL light when the gas tank gets 1/2 empty.

I will ask them how they arrived at the present diagnosis and if they put the engine on an analyzer and read the sensor traces- how else would they have been able to diagnose the truck with the coolant fan clutch problem?

You think it can be fixed? I used to think so too.

I will try your suggestions on the gas cap. My boyfriend guessed it was the charcoal filter as well but I will ask them to check the evaporative emissions control system too.

I do think it can be fixed, and I understand your frustration. You’ve struggled and done everything right and still the light comes on.

I’m guessing (and hoping) there are two things going on here, one being that nobody has yet really dug deep into an analysis, and the second being that a simple inability of the tank to breath in is causing a light and confusing the situation.

I sincerely hope my guess is right.

Maybe Dr. Gregory House can drop by the dealership and give the mechanics some pointers in diagnostic techniques. If they can’t diagnose something as simple as a radiator cooling fan which won’t shut off…good Grief!
I’m not convinced that the mechanics know the difference between a “standard” oxygen and an air/fuel oxygen sensor. Their electrical behaviors (the sensors’, not the mechanics’) are much different from each other.
Untill “Larry” comes back from vacation, I don’t know if they are going to make any progress on these problems. I hope some mechanics are doing some studying.