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Old 02-25-2011, 07:41 PM   #1
Dalamar
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Dizzy Inspection computer can't read my car, but I can. Bad PCM?

TL;DR the inspection computers at two shops can't read my computer, but I can. Why?

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I tried to get my 96 SL2 inspected yesterday, and was told that my car's computer was not responding to their inspection computer's attempts to connect to it. At the time I didn't know what to make of it but I thought later about something the guy had said - that the engine light didn't come on when he turned to key to verify that it worked. I figured from that that they must not have turned the key to the second position, since nothing but the radio works at the first click.

I know the OBD port works because I have my own scanner, an ELM327 clone that I use with a laptop, and can check my codes and view the monitors in realtime any time I want. It always works fine, as long as the key is in the second position or the engine is running. I get nothing in the first key position, which I assume is normal.

Today I went to a different place to try to get it inspected, and they had the same problem, but this time with the car running. Their computer sits on a screen with a timer counting down for two or three minutes, and then times out with an error message saying it can't communicate with the car. We tried several times and the only time it seemed to work was once when he started the test with the engine off, key on, but he said that that was not acceptable because it would not pass unless the engine were running. He was doing a dry-run test to make sure it would pass before submitting it to the state.

I still don't know if the first place actually had the same problem or if they just tried to start the test with the key in the first position, but I am assuming that if the test requires the engine to be running then they would have tried it that way, and if they did then it should have worked.

Is there some special test procedure to be used with Saturns? Are they supposed to be initiating the connection with the engine off, key on and then starting the engine at some point after that? Is their computer sending some sort of different message than mine that is confusing the car? Is there anything I can check with regard to the PCM or its wiring to see if something is loose or not connected properly?

I'd appreciate some insight into this bizarre problem. Even if it passes mechanically, it won't do me any good if they can't test the computer.

Last edited by Dalamar; 02-25-2011 at 07:51 PM..

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Old 02-25-2011, 09:01 PM   #2
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

When you turn the key to on the test site should connect to the PCM. If you connect the test computer and then start the car it will also connect to the PCM. This sounds like they have a well worn connector on the end of the test computer cable.

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Old 02-25-2011, 10:09 PM   #3
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

This is a 2 part problem. The connector in the car has aged and the test station is severely worn. As your reader connects I would suspect the test station. Try another station and bring your code reader. If they can comprehend that it is their problem they should be able to address it.

It makes no difference as to when you connect, key on or running makes no difference.

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Old 02-25-2011, 11:38 PM   #4
Dalamar
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

It doesn't work for me in the first key position, never has, but I don't know what that position is labeled or if it's supposed to work there.

I checked my codes in front of the guy with my own computer, so he knew it works, but had no answer as to why his didn't.

Perhaps it would help to clean the contacts on the connector. I will try this. As I said, I tried two different places, but since they service a lot of cars I suppose the both probably have dirty equipment.

Can the OBD connector be disconnected from the car, or is it part of some larger mass of wires that can't be separated? It would make it easier to clean, and this also makes me wonder if it might need to be replaced at some point.

Thanks for the quick answer.

Last edited by Dalamar; 02-25-2011 at 11:45 PM..

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Old 02-26-2011, 12:48 AM   #5
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

Be very careful cleaning contacts. You can destroy the PCM or SDM. No metal and no sandpaper and do not short any pins together. Pin 2 and pin 16 are the only ones you care about for the PCM data. The first drawing is the pin diagram of the connector and the 2nd is the electrical diagram and the square boxes in the lower center are the connector. The best thing to use is an old style large red rubber eraser and rub lightly then clean with alcohol on a Q-tip.

The connector is part of a harness. It is not hard to clean in place. If you look you will see a raised area on each contact. Only the raised area needs to be clean and if they look clean then just clean them off with the alcohol Q-tip.
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Old 02-26-2011, 12:56 AM   #6
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

That's why I wanted to know about removing it, I figured it would be safer to clean if it weren't hooked up to anything. If not then I'll just do the best I can with it in place.

Thank for the pinout and schematic. Always good to have more info about something on is working on.

On other peculiarity about my PCM - if I restart the engine immediately after clearing codes, it only clears failed monitors. Those that have passed stay in place so I don't have to drive around to reset them. Is this normal?

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Old 02-26-2011, 01:07 AM   #7
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

Probably. The connector is held in place with 2 screws. You can remove the screws and the connector will drop down and the wires are lone enough to get a better look art it. You can remove the PCM B fuse to remove power from the connector but that will also reset your monitors. The EVAP monitor will not run unless the fuel level is between 25% and 75%.

Where are you located in TX?

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Old 02-26-2011, 01:13 AM   #8
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

Deer Park, just outside Houston.

I can clear the monitors by not restarting the engine after I tell it to clear them. At least, I've done it in the past, using the scanner. My concern was that this phenomenon of only clearing the bad ones was an indication of a PCM problem, as I didn't think you were supposed to be able to do it that way. I figured there was just on OBD 'reset' command that cleared everything, so since that isn't happening I was wondering if it might point to a PCM problem.

Not that I'm complaining about it. It's very convenient to be able to reset a code and see if it comes back without having to worry about trying to get the others reset afterwards.

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Old 02-26-2011, 01:19 AM   #9
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

If you pull the PCM B fuse in the UHJB, engine compartment fuse box, before cleaning pin #2 that will reset all of them. After the cleaning you can do a hot lap on the Sam Houston Tollway, that should get them all reset. Or the 610 at rush hour. You pull the BODY fuse in the inside fuse panel to de-energize pin #16

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Old 02-26-2011, 01:26 AM   #10
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

Okay, good to know. I just though that selectively clearing things was abnormal, or might be a sign of PCM failure. If not then so much the better. One less thing to worry about.

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Old 02-26-2011, 01:32 AM   #11
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

There are only 2 pins that they will pull data from. Power from #16 and the actual data from #2. If you have a voltmeter I would check pin #16 to ground for 12V Be careful as arcing is not good. There is a ground pin in the connector also you can use.

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Old 02-26-2011, 01:38 AM   #12
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

I have a meter, and the thought just occurred to me that maybe if it's dirty or for some reason not putting out enough power that the reason it works for me and not for them is that my scanner gets some power from the USB port. If it is the power pin that's dirty, maybe their machine is failing because it's not seeing the clean 12v that it expects, whereas mine has a little bit of help from the other end. Dunno how reasonable that is, but it's a theory.

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Old 02-26-2011, 08:38 AM   #13
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Default Re: Inspection computer can't read my car, but I can. Bad PCM?

Depends on what the test scanner is expecting. Carefully check the voltage between the pin #16 and #4. Remember connecting 12v to the wrong pin is not good at all. Verify 12v to the car ground and then verify the connector ground to the car ground. You can look on the back of the connector and the wire colors are going to match when you find the right pins.

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