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GM Tech (Cam)
GM Tech (Cam), Auto Service Tech
Category: Car
Satisfied Customers: 29503
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2002 Chevy Impala: overheating..the air box (with the ECM in it..crank

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2002 Chevy Impala, 3.4, Will Not Crank

I was working on an overheating problem with this vehicle and among other things changed out the upper and lower radiator hoses. The upper hose change required me to move the air box (with the ECM in it) to one side. This may or may not be related, but now it will not crank.

I did some research, used a 2.2k resistor across the yellow and black passlock sensor wires going into the BCM, did the relearn process, got the security message to go away, and it still does not crank. After another battery disconnect/reconnect the security message has returned.

What's more, it does not talk to my Innova 3140 code reader. I have confirmed continuity from the PCM to the DLC on the serial data line and the associated ground line. I have tried a different PCM (used). I am also getting a "service vehicle soon" message, and out of curious frustration disconnected the PCM from the vehicle and turned on the key. The results are identical, it's as if the PCM isn't there.

I have confirmed 12VDC at the battery voltage pin of the PCM, and checked continuity to my ground points. The related fuses all look good. The big puzzle is why it won't crank, but I also don't understand why my reader can't talk to the PCM. I have a fairly strong electronics background, and am being tempted right now to go more into computers simply so this sort of thing doesn't floor me again! Any assistance would be appreciated
Chat Conversation Started
GM Tech (Cam) :

I will do my best to assist you. When you are finished please click on accept only if you are satisified. I don't get paid unless you do.Please do not accept if you cannot leave positive feedback. I don't know if you are a tech or a just working on your own vehicle so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answers will be based on what you tell me so please add all the details you can.

GM Tech (Cam) :

Does the check engine light show in the dash when you turn the key on?

Customer :

No. But come to think of it I have more of an information center, and among other things am getting a "service vehicle soon" message.

Customer :

I am not an experienced car tech, so I may need you to define some terms. When you say ignition power, do you mean is the PCM being supplied with 12vdc when the key is on? If so, yes.

GM Tech (Cam) :

OK and battery power?

GM Tech (Cam) :

yes that is ignition power. THere is B+ and IGN+, both are 12V. YOu are using a meter or a test light?

Customer :

I am using a meter. I don't recall an IGN+ on the schematic, but will be happy to check and get back to you. Are you looking at a print? If so, then we could save a step with you telling me connector and pin number.

GM Tech (Cam) :

YEs, one moment.

Customer :

Just a minute. My computer and car are in different places. I can tell you I've got 12V at C1 19, nothing in C2 24, and the connector printout and the schematic have different opinions about what's at C1 20, but I don't think I even see a connector there. Will double check. Is it OK to check these voltages against battery negative terminal?

GM Tech (Cam) :

Against battery neg or solid ground.

GM Tech (Cam) :

Full Size Image

Customer :

Okay, don't know why I convinced myself about that pin 20. Nothing. Fuse is okay, have 12V there, so now I have a broken wire to ring out. Before I gratefully hit "accept", any other advice?

GM Tech (Cam) :

Nothing in pin 20?

GM Tech (Cam) :

That is fuse is ok?

Customer :

Correct. And I have 12V at that 15A fuse. As I said, it all started when I pushed the air box out of the way to change the upper coolant hose. Vehicle has seen 250K+ miles. I may have broken a wire or the junction at the connector is damaged.

GM Tech (Cam) :

Yes, that is what I expect, broken wire.

Customer :

That brittle, huh?

GM Tech (Cam) :

After that many miles, it can fatigue.

Customer :

Sometimes so helpful to have someone look over your shoulder. Thanks a bunch. Can I hit accept now?

GM Tech (Cam) :

You can reply at any time for follow up information regarding this issue, even after you accept my answer and I will reply.

Customer :

I've never used a service like this. Can I leave the site and come back to this conversation?

GM Tech (Cam) :

yes.

Customer :

How?

Customer :

Ah. My email. One other quick question. I use Alldatadiy. Cannot manipulate the images, yet you were able to send one to me. Through this ordeal I was wishing I could piece together a "master" schematic around my problem. What program did you use?

GM Tech (Cam) :

mitchell on demand.

Customer :

I'll look into it. Thanks again. I'm off to fix a wire.

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