3 replacements of O2 sensor and still have P0134 code. Now told it is the PCM

Here is my backstory:
I have a 2002 Chrysler T&C limited. In September 2012, squirrels chewed through the wiring to my bank 1 O2 sensor. After a quick and easy fix, there were no issues or codes. In February 2013, three error codes popped up (P0134, 0138, 0139), and the car was running sluggish and getting poor gas mileage. Three weeks ago, I took the van in to replace the O2 sensor. (I did not drive more than 40 miles since the codes came up). I got the van back and all was well, until 10 minutes into driving and the P0134 code returned. I took the van back and the dealer replaced what they called, “a faulty O2 sensor.” I picked up the van last weekend and they assured me everything checked out; they test drove it a few miles and no codes. Sure enough, after 10 minutes of driving the code reappeared again. Took the van back a third time and today I was told they replaced the sensor a third time, but found too high a voltage going to it. They are now saying I need to replace the PCM. I am trying to see if it could be anything else before I pay out $1000 for the replacement PCM.


It is time to take the van to another shop for a second opinion

Do NOT tell them the first shop condemned the PCM. Let them arrive at their own diagnosis.

In my professional experience, the PCM is seldom the cause

Nevertheless, they often get replaced needlessly

But if the second shop arrives at the same diagnosis, it may be the exception to the rule.

The O2 sensor produces it’s own voltage. The lower the voltage is the more oxygen there is in the exhaust gasses. The higher the voltage is the less oxygen there is in the exhaust gasses. If the voltage from O2 sensor is always reading high it means it’s not reading the oxygen content in the exhaust gasses.

If you have to drive 10 minutes before the Check Engine light comes on with the same code with the new O2 sensors, then the O2 sensor may be getting coated or contaminated where it can no longer read the oxygen content in the exhaust gasses and the voltage signal from the O2 sensor remains high. A couple of things that can cause an O2 sensor to become contaminated are coolant leaking into the combustion chambers or a silicone sealant was used on the engine that wasn’t sensor safe.

I would check to make sure the new O2 sensors aren’t being coated/contaminated with a substance of some kind.


The O2 sensor does produce its own voltage, but there are also two wires that run the sensor’s heater. The heater is necessary because the O2 sensor only begins to actually work properly when it gets to around 800 degrees F, and it takes a long time for the exhaust to heat it this much, so an internal heater is used to speed things up. If the squirrel chewed through all the wires, it’s possible that the heater wires were shorted to the signal wires, or shorted to each other, which could possibly damage the PCM. I’m not saying the PCM is bad, just that it’s certainly possible.

That said, I second the motion that you take the vehicle elsewhere. You should be able to get a re-manufactured or salvage PCM for far less that $1000 if that’s the problem. There is no reason to use the dealer for repairs on a 12 year-old van unless you have a warranty with them. They will almost always be more expensive than an independent shop, and not necessarily more competent.

I would suspect a broken wire more than a bad PCM. I would have someone go through the repairs to the wiring first in case one of the splices didn’t take.

It’s a common problem that when the code refers to the O2 sensor, then the shop simply replaces the sensor. But the problem in many cases is not the O2 sensor. And when the set of them are replaced for no reason, you end up with a car which now has non-OEM sensors, which aren’t as good of quality as what you had in the first place.

There are procedures for finding out what is wrong. You just need to find a shop who has the tooling and expertise to do them for you. And one who doesn’t engage in replacing parts for no good reason. This is likely a fuel mixture problem that is being reported as a sensor problem simply because the sensor is detecting the air/fuel mixture problem. Or the sensor heating circuit has failed for some reason.

First off, you need a shop who owns the Chrysler-specific scan tool. The shop with this tool can tell a lot what’s going on by, first looking at all the codes current and pending, then looking at the real time engine parameters like fuel trim, O2 levels in each bank, before and after the cat. The actual problem may be something like the MAF or a faulty injector or air leaks, allowing unmetered air to bypass the MAF. An exhaust leak, like a cracked exhaust manifold, as well as a slew of other issues can cause this symptom too.

Did you consult Cons Reports magazine on this car before you bought it? Your problem might be expected. Maybe take a look and see how CR says this 2001 car’s fuel system reliability is reported by other owners.

One final thought. Unless the shop has all the needed tooling and expertise, I very much doubt the problem is the PCM; but whatever is causing this, it has to be corrected, as continued driving with this problem uncorrected may also damage the cat, which will prove to be an even more expensive repair.

And try to get the shop to install the old O2 sensors. Unless they purchased OEM versions from Chrysler, the old sensors are probably better than the new ones recently installed.

@GeorgeSanJose: Most Chrysler vehicles seem to use MAP sensors instead of MAFs. These will compensate for air leaking in. But you are absolutely right in that O2 sensor codes are not necessarily from bad O2 sensors at all, but a symptom of another problem.

Good point @oblivion. My Corolla uses the MAP method. Seems to work fine. Never had any trouble with that part in 20 years and 200K of use. The other engine available in the same production year, with a higher displacement,compression, & power, it used the MAF method. I presume there are reasons why when comparing the MAP vs the MAF, why one is better than the other. I expect the MAF works better in situations where there is a lot of air flow, like w/high power & turbo engines. It may be the manufacturers prefer the MAP because it is less expensive, but need to use the MAF to meet emissions standards in certain of their engines. That’s my guess.