Electrical starting issue
Fleet Owner
Joined: Nov 2003
Posts: 27,916
Likes: 3,635
It is probably OK since the fuel pump came on, but I can't recall for sure. I truly think it is specifically the TRS system, but I would like to see that fuse and the fan wiring checked to just make sure (at the fan clutch and in the wiring harness under the air filter).
The PCM has separate 12V systems and the manuals don't get very specific on the PCM internal circuits - at least from what I can tell.
The PCM has separate 12V systems and the manuals don't get very specific on the PCM internal circuits - at least from what I can tell.
Fleet Owner
Joined: Nov 2003
Posts: 27,916
Likes: 3,635
He is not getting the reverse lights when he shifts into reverse.
I see two possibilities:
The Manual shows that the TRS is fed by circuit 371 (12V) from the PCM.
The Fan is fed (12V) from circuit 361 from the CJB (fuse 2.22 feeds circuit 361). This is the power that would activate the fan clutch relay (when the PCM grounds the circuit) That circuit also feeds VPWR (12V) to the PCM.
#1 .... It is possible (maybe likely) that if the VPWR TO the PCM is compromised, then any 12V power from the PCM will be impacted. That said, the only thing that is unclear at this point, is how that would affect the PCM's ability to process information (like the position of the transmission) and then consequently activate the ground circuits when appropriate.
#2 .... Also possible: The PCM provides buffered 12V power to the fan clutch to operate it through circuit 352 (duty cycled). Perhaps this buffered power is generated in the same components of the PCM as the 12V buffered power supplied to the TRS. If so, any short in this wire would affect the TRS power feed.
Both of the above conditions would cause a NO-CRANK.
Thanks for suggesting to contact Keith. I'll try to get my thoughts organized and see if he could help.
As far as this thread goes, hopefully we can get some questions answered soon...................... Afterall, the first step of checking a fuse is as easy as it gets!!!
If fuse 22 and the fan wiring look good, the next step for the OP is:
Verify good 12V power TO the TRS (from the PCM).
note: if that power TO the transmission connector is good, then I would have to believe that the issue is the TRS itself, perhaps the wiring inside the transmission, or the wiring that sends the TRS signal back to the PCM. To check these circuits all you need is a Multimeter, the correct leads, and small back probe pins. Fairly easy to do.The circuits to back probe for 12V power (with key "ON", or when trying to crank) would be:
2. pin # 21 at the transmission connector C1385 (Pink w/ White stripe wire on both ends).
If 12V buffered power is present going TO the transmission, then the issue must be in the TRS sensor, the internal transmission harness, or the wiring to the PCM from the TRS ...as hypothesized above.
Hopefully the OP will take the troubleshooting this far, but if not, it is here for others.
I see two possibilities:
The Manual shows that the TRS is fed by circuit 371 (12V) from the PCM.
The Fan is fed (12V) from circuit 361 from the CJB (fuse 2.22 feeds circuit 361). This is the power that would activate the fan clutch relay (when the PCM grounds the circuit) That circuit also feeds VPWR (12V) to the PCM.
#1 .... It is possible (maybe likely) that if the VPWR TO the PCM is compromised, then any 12V power from the PCM will be impacted. That said, the only thing that is unclear at this point, is how that would affect the PCM's ability to process information (like the position of the transmission) and then consequently activate the ground circuits when appropriate.
#2 .... Also possible: The PCM provides buffered 12V power to the fan clutch to operate it through circuit 352 (duty cycled). Perhaps this buffered power is generated in the same components of the PCM as the 12V buffered power supplied to the TRS. If so, any short in this wire would affect the TRS power feed.
Both of the above conditions would cause a NO-CRANK.
Thanks for suggesting to contact Keith. I'll try to get my thoughts organized and see if he could help.
As far as this thread goes, hopefully we can get some questions answered soon...................... Afterall, the first step of checking a fuse is as easy as it gets!!!
If fuse 22 and the fan wiring look good, the next step for the OP is:
Verify good 12V power TO the TRS (from the PCM).
note: if that power TO the transmission connector is good, then I would have to believe that the issue is the TRS itself, perhaps the wiring inside the transmission, or the wiring that sends the TRS signal back to the PCM. To check these circuits all you need is a Multimeter, the correct leads, and small back probe pins. Fairly easy to do.
note: the two steps below are to check if 12V power is being sent from the PCM to the transmission harness that feeds the TRS.
1. pin #1 on PCM connector 1381b (we've suggested that one in other threads - it is the connector closest to the vehicle front), and2. pin # 21 at the transmission connector C1385 (Pink w/ White stripe wire on both ends).
If 12V buffered power is present going TO the transmission, then the issue must be in the TRS sensor, the internal transmission harness, or the wiring to the PCM from the TRS ...as hypothesized above.
Hopefully the OP will take the troubleshooting this far, but if not, it is here for others.
Thread Starter
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Mountain Pass
Joined: Jan 2009
Posts: 185
Likes: 1
Took some time off for Christmas and just got back to work. Fuse 22 is good. Fuel pump comes on with the key.
Rainy here today and I don't have an indoor space to work on the truck so I will try to follow your further instructions asap. This may be beyond my capabilities but I'll try. Thank you again.
Rainy here today and I don't have an indoor space to work on the truck so I will try to follow your further instructions asap. This may be beyond my capabilities but I'll try. Thank you again.
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