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Discussion Starter · #1 ·
OBD came back with a Speed sensor code, which was then replaced, along with the harness. Mechanic suspects it might be a faulty ECM, but he said he cannot help me any further. Car has been starting rough lately not sure if that has anything to do with the issue. The limp mode happens very randomly, but always after a full stop (most of the time at a red light) it gets stuck in first gear, the speedometer stops working and the anti-lock light comes on. Couple times it resolved itself after turning the car off and letting it sit for a bit, another time unplugging the battery and wiggling the wires helped. Has this happened to anyone else? I am looking for any input as I've put so much money into this van already and nothing seems to be helping.
 

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Common Sense + Critical Thinking
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Make sure your grounds are clean and tight.

What was the speed sensor code, and did it come back after replacing the harness/sensor?
 

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Discussion Starter · #3 ·
Code came up as P0502 and I haven't checked after replacing the parts but I assume it would since the same exact thing keeps happening. I haven't looked at the van in a few days, we had a snow storm and bad weather, but I can take a look and see if its still locked up and run the codes again.
 

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Common Sense + Critical Thinking
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Code came up as P0502 and I haven't checked after replacing the parts but I assume it would since the same exact thing keeps happening. I haven't looked at the van in a few days, we had a snow storm and bad weather, but I can take a look and see if its still locked up and run the codes again.
If they replaced the VSS, it's most likely good and the problem rests in the connectors/wiring.
Do you have the GM Techline eSI from: Info Share - Owners/Service/Parts Manuals - Wiring Diagrams
 

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Common Sense + Critical Thinking
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You can test it at the PCM connector.

There could be a problem anywhere in the wiring between the sensor and the PCM.
 

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Remove the connector from the PCM and measure the resistance between terminals 29 and 30 on C1.

Does this happen quite regularly or is it mostly random?

I would also check/clean/tighten your engine grounds, esp the on on the rear of the engine near the knock sensor, kinda below the oil pressure sensor.
 

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Discussion Starter · #11 ·
Remove the connector from the PCM and measure the resistance between terminals 29 and 30 on C1.

Does this happen quite regularly or is it mostly random?

I would also check/clean/tighten your engine grounds, esp the on on the rear of the engine near the knock sensor, kinda below the oil pressure sensor.
It happens when the car is stopped at a red light for an example, then the speedometer stops working and the car gets stuck in limp mode.
 
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