When installing a used VCM to my 2000 blazer, will it need to be reflashed or will it be "plug and play"?

 

It will need to be flashed to your VIN. These PCM's rarely fail, unless of course someone went to the trouble of intentionally causing the damage. Why are you replacing it?

 

I have a po740 code for TCC circuit failure. It is the only code and is permanent. I have power to the trans connector, checked and I have continuity on the ground side from the connector to the VCM. I installed a new TCC solenoid. Can't think of anything else it may be.
Will the VCM be inoperative without flashing?

 

These PCM's are darn near bulletproof and they rarely fail. It should not be replaced unless following the diagnostic flow chart specifically instructs you to replace it. Each PCM is programmed for the specific vehicle that it was installed in, with the exact options, (RPO codes) that the vehicle was equipped with. If you can find a vehicle with the same RPO codes as yours, it will work, provided it's good . The odds of finding one like that are slim though. Even if you were able to find one, it would still require the crankshaft position sensor relearn to be performed with a high end scan tool.


When the PCM detects a continuous open, short to ground, or short to power in the TCC solenoid valve circuit, then DTC P0740 sets. There are several things that can cause that, and you've checked a few of them already. Here is the flow chart: https://blazerforum.com/forum/diagno...plained-28391/ Some of the tests require a bi-directional scan tool, but with some logical diagnosis skills, you can usually work around them. More than likely you'll find a circuit problem such as: ignition switch, open circuit, stop lamp switch, etc. Follow the chart and see what you find.


The TCC solenoid must have battery voltage with the ignition in the RUN position. The PCM applies ground to operate the solenoid. The harness to the trans, and the harness inside the trans, need to be inspected closely, they both are susceptible to issues.

 

Thanks for the info. I have run throught the flow chart, I have a snap on scanner that allows me to activate the solenoid. with the vehicle on the lift I can activate the TCC solenoid and it does engage. That tells me that the actual TCC circuit is good correct?
I measure 21.5 ohms throught the solenoid circuit at the trans connector.

 

I also have 1.5 K-ohms through the ground side of the circuit, trans harness through vcm, key off. Is that correct? I would think I should have 0 continuity.

 

If you can hear the solenoid, the circuit is good. Whether the solenoid is actually moving the valve is unknown though. Is the PCM seeing the stop lamp signal come on and off? Your scanner will show it.

 

Yes, brake pedal signal is "closed" at rest and "open" when depressed. I have also noted the PWN TCC is at 96% duty cycle almost constantly except at idle when it is 0.

 

I'm assuming the VCM is monitoring voltage drop through the solenoid circuit, so would it even matter whether the valve actually moved or not? The code sets within 10-15 seconds after startup without even engaging the trans.

 

This would indicate a circuit problem. When the PCM detects a continuous open, short to ground, or short to power, P0740 will set.


Check resistance on both wires. Both end to end, to each other, to power, and to ground. You'll need to check each one individually, while totally disconnected from battery voltage and the PCM.


Yes, TCC duty cycle should be 0% at idle.