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Discussion Starter · #1 ·
My son drove truck for a while well one day he went to the store turn it off he eent in the store for 20 min tried to start nothing. Checked the battery, fuses, everything was good still no crank, no start. Then I noticed the shift indicator was in 3rd but the shift was in park. So I pulled the truck home check out everything. The only code it my scanner shows is 0606 PCM fault. I checked the grounds, then jumped the starter relay with my power probe the truck started but missing real bad and it was in reduced power mode, replaced the neutral safety switch still nothing changed. Well I started looking at the wiring and found the blower motor harness burnt and melted under the dash. I replaced it with a new plug w resister. Still wont turn over with the key. So i reset everything by pulling the battery cables off and touching the + & - together for 30 mins. Then I put the cables back on the battery same shit. So I jumped it at the starter relay again it started but missing real bad and now i have no throttle and Its still shows 3rd on the cluster. I can shift the gears and the truck will go in all gears but the indicator doesnt change from 3rd on the cluster. Im thinking maybe I have a short to ground on the transmission harness but I cant find any damaged wires. Did anyone have these issues before? Or can someone tell me what I need to do next?

Thanks Duston Fell
 

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Maybe the switch has an internal defect? I'm not sure why it is called a PNP (Park Neutral Position) switch. The switch contains the circuits that tell the PCM what position the shift lever is in i.e. Drive, Reverse, Low, etc as well as neutral and park.
 

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Discussion Starter · #8 ·
The original switch that i replaced was doing the same thing so I bought then installed a new switch no change. I may be wrong but I dont see that the switch would be defective in the same way as the old switch. I dont know if it has a code for the PNP switch but the only code is 0606 PCM Failure. But the truck has always had that code for years according to the previous owner. Do you think that it could actually be the PCM or BCM that failed?
 

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I agree. Even if the switch is aftermarket it probably would not have the same fail.

Let's regroup. You have a truck that won't start. Most likely cause, based on the symptoms, is that the PCM is not seeing that the transmission is in the correct shift position. Or the PCM is not reacting to a correct signal from the PNP switch.
The instrument cluster shift indicator does not move from one position. The indicator is controlled, by the PCM, using the Serial Data Bus. Almost all functions of the cluster are controlled by the Serial Bus and no other problems have been reported regarding the cluster. Therefore we can assume that the Serial Bus is operating and the PCM can change the shift indication, if it wants to.

DTC P0606 could be a failure internally in the PCM, a power failure or a defective ground.

Now, there appears to be either a problem with the PCM or the PNP switch. It is going to require some troubleshooting, but before that there is one more thing to try. The ground point for both the PCM and the PNP switch is G102. Maybe remove the bolt and clean the area and check for broken wires. On the left (driver's side) of the engine block, below the starter and down near the oil pan, there are three ground points in a row. G102 is the aft one. Might as well do all three while you are there.

If there is no change after checking that, you will need a multimeter and some backprobe pins for troubleshooting the wiring. Determining that the PCM could be defective requires eliminating all other possible sources for the problem.
 

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Discussion Starter · #10 ·
I agree. Even if the switch is aftermarket it probably would not have the same fail.

Let's regroup. You have a truck that won't start. Most likely cause, based on the symptoms, is that the PCM is not seeing that the transmission is in the correct shift position. Or the PCM is not reacting to a correct signal from the PNP switch.
The instrument cluster shift indicator does not move from one position. The indicator is controlled, by the PCM, using the Serial Data Bus. Almost all functions of the cluster are controlled by the Serial Bus and no other problems have been reported regarding the cluster. Therefore we can assume that the Serial Bus is operating and the PCM can change the shift indication, if it wants to.

DTC P0606 could be a failure internally in the PCM, a power failure or a defective ground.

Now, there appears to be either a problem with the PCM or the PNP switch. It is going to require some troubleshooting, but before that there is one more thing to try. The ground point for both the PCM and the PNP switch is G102. Maybe remove the bolt and clean the area and check for broken wires. On the left (driver's side) of the engine block, below the starter and down near the oil pan, there are three ground points in a row. G102 is the aft one. Might as well do all three while you are there.

If there is no change after checking that, you will need a multimeter and some backprobe pins for troubleshooting the wiring. Determining that the PCM could be defective requires eliminating all other possible sources for the problem.
Now we on the same page. I had already checked all other grounds I could find. But not the ones you just told me about. This sounds like that could be the issue so when i get home today I will differently check this and let you know. Thanks man !
 

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Do you have a multimeter? You will also need some pins to backprobe the connectors. There are pins made for the purpose of backprobing, but you can get some straight pins or T pins from a place that sells sewing supplies. Let me know when you are ready to start. The only way to tell if the PCM is bad is to eliminate any problems with the circuits to the switch. You will have to check power going from the PCM to the switch and to make sure the switch has a good ground.
 

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Well, maybe recheck the grounds again. Especially the aft one (G102). The DTCs you posted are all for circuit issues with components that have their grounds inside the PCM. In other words, if the PCM is not getting a ground, those circuits are not getting a ground. If those codes are new, the problem has to be related to something you just did. Maybe one of the wires was already weak and just broke. Check for swollen wires that would indicate corrosion under the insulation.
I sent you a message regarding troubleshooting.
 

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Discussion Starter · #16 ·
The grounds were all good. I had to leave for work early. So I brought it to a local GM dealer. Ill be gone for 2 weeks so they'll have plenty of time to figure it out. Ill update the post once the repairs are made. Thank you Cart7881 for all your help it is greatly appreciated!!!!
 
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