Bad PCM. Questions before the swap. P0606.

[toby1234]

Hey guys. So Ive been searching the forum and looks like a P0606 code is known to actually be a bad PCM. Here's the story leading up to this. Last saturday, car started up at 6:30am without issue. Five hours later, I get in, crank the engine, and the battery is low. I used a jumper and the car started right up. When I put it in reverse, the car went into etc fail safe mode and would not engage reverse. I then put it in drive, drove it home and parked it.

This is the second time this happens. First time happened about 6 weeks ago. That time, I simply charged the battery and all went back to normal. I tested the battery and it was good. This time however, after charging the battery, I tested it and it was bad. Tested the alternator and its good. I have a feeling something made the battery go bad prematurely. Why else would it start up fine in the cold morning but struggle 5 hours later? Also, no starting issues prior to this.

So I stuck another battery in there and when I turn the ignition to ON, the radiator fan comes on. When I try to start it, the engine cranks but does not start. Sounds like no fuel to me and from what I've read on here, thats exactly whats going on. The red anti theft light blinks fast while the engine cranks as well. So I press the unlock button on the key fob to see if its related and sure enough, the car will now start. Problem is, idle shoots up to 3k rpm and if I shift to reverse, idle drops to less than 800rpm, etc failsafe comes on, and the engine starts to misfire.

These are the codes I recovered. P0606, p2107, p2106, p2196, and p2198. I came on here and Ive been searching for the past few days, trying to gather as much info as I can find. I replaced all the coils and plugs about 3 months ago. Like an idiot, I did not listen to the vets on here and I used cheap ebay coils. Although the car ran fine for that time, those coils probably ruined the PCM.

I know I need to get another PCM and take it to a dealer to have it married. What are my options for getting a second key? I only have one. Also, I will most likely replace the coils and plugs soon after even though the cheap coils "seem" to run fine. I checked the primary and secondary coils on each and they were all above the minimum resistance. I have no way of stress testing them. Should I replace them first just in case its the coils and not the pcm? I ask because Im not sure if bad coils would cause issues BEFORE the engine starts. Would bad coils interfere with the PATS and keep the engine from starting? Thank guys!

 

[joegr]

So, you believe that the e-bay coils killed your PCM (certainly possible), but you want to give them a chance to kill the new PCM? That doesn't make any sense to me. I'd replace the coils and plugs first. Use OEM coils this time. And, yes you need to replace the plugs again even though you just did it. Of course, you can try cheaping-out again. Maybe it'll work better for you this time than last time.

If your dealer doesn't cut keys (not all do), you'll have to buy a key from a Locksmith. If you're smart, you'll buy two new keys. Then, if something happens to one later, you can still add another yourself without having to pay the dealer again.

What level of testing did you do to decide the alternator was good? Did you check for AC voltage (shorted diode)? Did you check it while driving around for a good while, or just for a minute with it idling?

 

[toby1234]

Thanks for your reply. I plan to swap to oem coils regardless. I just want to figure out how to approach all this first. When I replaced the coils 3 months ago, I did not encounter all these issues. I replaced them because I could feel the engine miss from time to time. Will bad coils cause these pre-starting issues? Will they trick the pcm into turning the fan on before the engine cranks?

I had the alternator tested months back and again just a few days ago. I used a tester at autozone. It tests the alternator for three things. Regulation, diodes, and output. All were good (results just say good or bad for each, no specific details). Any issues with the diodes would have failed that particular test. If any of the three fail, it labels the alternator as bad. Ive tested the voltage at home when the car is cold and after a short drive. Its always been around 14.3v volts at the battery. Of course, that is DC voltage. I'll look into testing the AC voltage. Would a bad alternator alone cause pre-starting issues? Ive also read on here that a bad alternator could damage the PCM too.

 

[joegr]

... Will bad coils cause these pre-starting issues? Will they trick the pcm into turning the fan on before the engine cranks?... Would a bad alternator alone cause pre-starting issues? Ive also read on here that a bad alternator could damage the PCM too.

Probably not directly. Look at this way. Coil or alternator damages PCM. Now car has starting problems.
It might only take one second for the new PCM to be toasted by the bad coils, if indeed this is the problem.

There's no tricking the PCM into turning the fan on with the engine not running. You need to understand how the fan works. When you turn the key on, it supplies power to the fan electronics (in the fan motor). The fan electronics look for a signal from the PCM to tell it to how fast to run, or not to run. If the fan doesn't see any signal from the PCM, then the fan turns on at max speed as a failsafe. In other words, the fan will come on when you turn the key on if the PCM is dead, or if the PCM isn't getting any power. (Did you check the PCM relay under the hood?)

 

[toby1234]

So I haven't had time to work on the car until today. Since the battery was bad, I left it out of the car this whole time (about 4-5 days). Bought a new one today and kept the old one. I threw the old bad battery in there just to check for current at the pcm fuse. I also wanted to check the pcm relay since joegr suggested it (thank you sir!). I pulled it along with the horn relay to compare the two. Their resistances were the same at similar terminals. So I stuck both of them back in their original positions. I have no way of testing them when hot. I decided to try to start the car again. I turned the ignition to ON and the fan did not come on. The car then started right up without issue. This is with the bad battery. No check engine light, but I could feel a misfire as it idled at the normal 800 rpms. Not nearly as bad as before, but still evident. I shifted into reverse and the car did what I asked. No etc fail safe.

The last time I had worked on it, I had also left the battery disconnected. During those days, however, it was only over night or until I could work on it again the next day. Those days, upon start up, the car would misfire pretty bad. Upon shifting into reverse, the car would automatically go into etc fail safe and reverse would not engage. Nothing has really changed in the passed week. The only difference is that the battery was left disconnected significantly longer than before.

Im going to order a new set of coils and plugs since they are probably bad regardless. I will be pleasantly surprised if that solves the problem. I highly doubt it though.

 

[joegr]

.... The only difference is that the battery was left disconnected significantly longer than before...

Five minutes or five years, the PCM wouldn't know the difference. This was not a factor. The thing that you are forgetting is that you removed and replaced the PCM relay. It's possible that the relay socket contacts (and/or relay terminals) are corroded. If so, your R&R probably scratched through some of the corrosion and made better contact. While this is theory, it is supported by some reports on here about issues with the PCM relay and socket. It would also support most of your symptoms.

 

[toby1234]

Interestingly enough, I had actually pulled the PCM relay two weeks back because I thought the fan relay was bad. I've had that happen on another car where the fan relay goes bad and keeps the fan on even after the key is out of the ignition. I pulled a few relays until the fan turned off. When I put it back in, the fan came back on and the throttle body opened and shut itself (I recognized the sound).

I did nothing more than remove and reinstall the same relay. Same as yesterday. It did nothing to help my situation then. At the time, I didn't know it was the PCM relay that I had pulled. They terminals were clean though on both the socket and relay. I'll try switching the PCM and horn relay next along with the new battery to see if it helps.

 

[joegr]

Interestingly enough, I had actually pulled the PCM relay two weeks back because I thought the fan relay was bad. ....

There is no fan relay on the LS.

 

[toby1234]

Haha I realized that yesterday, after looking at the manual. That's when I found out it was the pcm relay. Most cars have fan relays. Of course, The LS is not like most cars.

Before swapping relays and batteries, I decided to turn the car on. I connected the bad battery, fan did not come on, and the car started right up. No idle issues. No misfires. No etc fail safe. Shifted into reverse without issue. I turned it off, swapped horn and pcm relay, started it up, and again, no issues. I swapped the bad battery with the new one and drove it to autozone. Tested the battery, starting, and charging system. Everything was ok.

WTF?
The old battery was recently charged and tested 3 times and failed the test each time. Although it still holds a charge and starts the car, I do believe its bad. So I'll leave the new battery in the car. I have a feeling that something caused the battery to go bad though. And although Im glad the car is now working, Im upset I have not located the issue. All I did over the last few days is plug and unplug things. Even the old "bad" battery still works fine with the car. I ordered new coils and plugs last night. Ill install them when they arrive. That should eliminate the coils as a suspect. I hope Im in the clear but I doubt I am. I dont know of many ignition coils that will work one day, misfire like crazy the next, and work just fine the day after that. Seems to me that something (pcm) is causing the misfire. Along with everything else. We'll see.

 

[LS4me]

Haha I realized that yesterday, after looking at the manual. That's when I found out it was the pcm relay. Most cars have fan relays. Of course, The LS is not like most cars.

Before swapping relays and batteries, I decided to turn the car on. I connected the bad battery, fan did not come on, and the car started right up. No idle issues. No misfires. No etc fail safe. Shifted into reverse without issue. I turned it off, swapped horn and pcm relay, started it up, and again, no issues. I swapped the bad battery with the new one and drove it to autozone. Tested the battery, starting, and charging system. Everything was ok.

WTF?
The old battery was recently charged and tested 3 times and failed the load test each time. Although it still holds a charge and starts the car, I do believe its bad. So I'll leave the new battery in the car. I have a feeling that something caused the battery to go bad though. And although Im glad the car is now working, Im upset I have not located the issue. All I did over the last few days is plug and unplug things. Even the old "bad" battery still works fine with the car. I ordered new coils and plugs last night. Ill install them when they arrive. That should eliminate the coils as a suspect. I hope Im in the clear but I doubt I am. I dont know of many ignition coils that will work one day, misfire like crazy the next, and work just fine the day after that. Seems to me that something (pcm) is causing the misfire. Along with everything else. We'll see.

A battery that fails a load test is bad. You'd be lucky to start the car!!

 

[toby1234]

Guess I'm lucky then? Either way, I installed a new battery. But like I said, car started right up with both.

 

[jammit]

Modern day batteries are not like 'good old days' batteries - a marginal one will often still start the car. Back in the 'good old days' you could get by for a while on a marginal battery by jumping it, charging it by driving around a while, and maybe get a couple more weeks out of it. With today's batteries, and all the electronics/computers/sensors in cars putting a load on the electrical system, if you gotta jump it once, replace it right then and there and save yourself the pain - seriously, it's not a good idea to jumpstart computerized automobiles - it IS however, a good idea to replace the battery before it dies as a preventative measure - just like sump pumps - it only dies when you need it most! Live and learn.

It's pretty well known that cars should have left the 12v system behind some years ago, as we did 6v systems in the 60's - it's just barely adequate anymore - but the legacy issues and costs to convert are holding manufacturers back from making the jump.

One other thing you're forgetting is to let the car re-learn it's idle fuel trim after pulling battery (or power to PCM) - there's a procedure for that. - look it up. It's probably why the car ran for crap the first time you started it after r/r the battery, and why it ran better on the second start.

I'd wager your problem was nothing more than a marginal battery from the beginning, which started a chain of events and a variety of transient symptoms in a very sophisticated, highly networked, multi-system-dependent automobile.

 

[LS4me]

Guess I'm lucky then? Either way, I installed a new battery. But like I said, car started right up with both.

Then if the car wouldn't run I would suspect a fail(ed/ing) alternator. A bad battery will kill the alternator.

 

[toby1234]

Well I've been driving the car for the past two days with the new battery and so far so good. Starts and idles fine. Only driven it about 20 though. I want to say it was the battery that caused all this but I'm not yet convinced. When it was giving me trouble, I installed a good battery from another car and nothing changed. Now that it runs fine, I can swap the new battery and bad battery and nothing changes either.

Like I said, the only real difference is that this time, the battery remained disconnected for 4-5 days straight as opposed to just over night. I know that some electrical components can remain charged for a while after a battery is disconnected. However, 8 hours should be enough to dissipate that charge (there actually is a difference between 5 minutes and five years). That should also be enough to reset the PCM. For now I'll chock it up to a bad battery. If I got lucky and the PCM is fine, then I feel like I dodged a bullet. Although there are no misfires right now, new coils and plugs are going in as soon as they arrive. I'd rather not push my luck with the eBay coils.

 

[joegr]

...(there actually is a difference between 5 minutes and five years)...

Well, I'm sure you've designed more of this kind of stuff than me then...

 

[toby1234]

And I'm sure you're being sarcastic haha. I based that statement on the fact that most people agree that the battery should be disconnected for a "while" in order to reboot the pcm. In my experience, five minutes is not enough (assuming all you do is disconnect the battery). I could be wrong though. Is five minutes really all it takes with the LS?

I appreciate all the help guys. Thanks for looking through here. I know it sucks that this forum has more problem threads than mod threads.

 

[jammit]

You're also supposed to short the + and - cables together for a few minutes when resetting the PCM/KAM (both cables disconnected from battery, and clamped together, just to be extra clear here) - another debated process (god knows why..)