2002 Explorer 4x4 PCM, OBD II, and Battery Replacement

[ttiwkram]

My 2002 Explorer's 4WD has died, so it's now just a rear-wheel-drive. (When was the last time your wife said her Explorer was "fishtailing" -- and she was right?)

Having read some of the other threads, the symptoms are familiar: One 4x4 light in the instrument panel illuminates momentarily at startup, and the 4x4 switches (to the left of the radio) have no effect at all. So, I'm pretty sure it's the good old PCM (Powertrain Control Module, or "4x4 Module").

I'd really like to be sure, though, which brings me to my question: If I buy an OBD II scanner, will a failed PCM give me a code to confirm the diagnosis? Or am I better off to just assume I'm right and order the ($$$) part?

Also - There have been several comments regarding PCM's failing in conjunction with (and presumably due to) vehicle battery replacement. Going on the hunch that it's due to a power spike hitting the PCM, I'm going to place a large capacitor from the + battery terminal to ground in hopes of reducing that spike. If it works, I may even leave it in permanently. I'd be interested in any comments regarding that approach.

Thanks in advance for your replies.

Mark W. in MI

 

[rrgone]

I can tell you that I never had my battery unhooked before my 4X4CM failed. I unhooked the neg. battery terminal after the 4X4 indicators started blinking and that stopped the blinking but not the loss of 4 wheel drive.

I also don't know if my Ex was throwing any codes before I replaced the module. My guess is that it was. I just went ahead and replaced it because I was willing to risk $150 for the pleasure of not taking it to the dealer. Why not take your Ex to AutoZone and have them hook it to ODBII for free? I never thought about that at the time. If you do get a scanner or get it scanned someplace please let us know what diagnosis you get.

 

[tbe2002]

Sounds like the 4x4 module behind the glove box attached the to the blower motor box to me. Dosen't sound like a PCM issue. I would just replace that module, it is a 10 min job and will fix the issue.

 

[ttiwkram]

PCM vs. 4X4 CM

Sounds like the 4x4 module behind the glove box attached the to the blower motor box to me. Dosen't sound like a PCM issue. I would just replace that module, it is a 10 min job and will fix the issue.

Yes, I've seen the 4X4 control module behind the glove box, and I think you're right. In that case -- just out of curiosity -- what's the Powertrain Control Mudule (PCM), and do you know where it is? I thought it was just a slang term for the 4X4 CM. My Haynes manual says the Powertrain Control Module is on the firewall behind the glove box, but it isn't.

 

[tbe2002]

Humm, I don't know where the PCM is located. I know on the 92 taurus I had it was behind the glove box towards the top of the firewall. Just look for a big wireharness going from the engine bay though the firewall, it will be at the end of that harness.

 

[Wüd]

I just had the exact same symptoms on my 2002. In fact, the wife's comment about fishtailing is what brought it my attention as well.

Removing the 4x4CM is very simple and it's even easy to get to. The replacement part was $151 from a friendly dealer in Nevada that this forum turned me on to.

The new module fixed the problem. I did NOT have any error codes when I scanned the vehicle. If you want to be double sure, just completely disconnect the 4x4CM. You will notice the behavior of the vehicle is exactly the same: No "4x4 High" illumination when you turn the ignition to the "ON" position.

The PCM is the general term given to the main computer control for the vehicle overall. If this was at fault, you should have the Check Engine light and thus some codes, along with some other major issues.

 

[ttiwkram]

Nevada Dealer Info?

Ah, yes. So the PCM is what used to be (more appropriately) known as the Engine Control Module, or ECM. That explains a lot.

Will you please provide contact information for that dealer in Nevada? His price is $50 better than anyone near me. So far I haven't been able to track him down.

Thanks!

Mark W. in MI

I just had the exact same symptoms on my 2002. In fact, the wife's comment about fishtailing is what brought it my attention as well.

Removing the 4x4CM is very simple and it's even easy to get to. The replacement part was $151 from a friendly dealer in Nevada that this forum turned me on to.

The new module fixed the problem. I did NOT have any error codes when I scanned the vehicle. If you want to be double sure, just completely disconnect the 4x4CM. You will notice the behavior of the vehicle is exactly the same: No "4x4 High" illumination when you turn the ignition to the "ON" position.

The PCM is the general term given to the main computer control for the vehicle overall. If this was at fault, you should have the Check Engine light and thus some codes, along with some other major issues.

 

[rrgone]

Check out the 4X4 Does Not Work thread. The vegas dealer contact info is in there. Be sure to give them your VIN number.