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2005 Chevrolet Trailblazer P0740, P0775, P1810 Fault Diagnosis: No 12V at Transmission Pink Wire

Model: 2005 Trailblazer Fault Code: P0740 Posted: 2018-02-09 07:48

Hello everyone! I'm new to this forum and recently purchased a 2005 Chevrolet Trailblazer. After driving it for about a week, I noticed the engine RPMs were higher than normal while driving. When I got home, I connected an OBD-II scanner and received fault codes: P0740, P0775, and P1810 (with another code not displayed). My first steps were to check fuses — all appear fine. I then tested the ignition switch, which also checks out. Next, I inspected the transmission connector under the truck. The issue is that there's no 12V reading on the pink wire at terminal E when the key is off or on. I’ve already verified the rear fuse box and confirmed that the 'ignition 0' fuse (10A) is good, with power present at both ends. I also checked the circuit from the transmission to the Powertrain Control Module (PCM), but no voltage is detected. Could this be a wiring issue? Is it possible that the PCM sends 12V to the transmission? If so, why isn’t it being received? I suspect either a faulty transmission solenoid or an internal harness problem. How should I proceed with troubleshooting? Any guidance on checking the solenoids or harness connections would be greatly appreciated.

Related fault codes
P0740P0775P1810
Comments (15)
Anonymous 2018-02-09 09:02

Check the rear fuse box — specifically, the 'ignition 0' fuse (10A) connected to terminal E at the transmission connector. Additionally, there is a second pink wire from the transmission to the PCM at terminal N. This connection is critical for proper operation.

Anonymous 2018-02-09 14:09

I'm currently at work, but I did check terminal E at the transmission plug. Could you please advise what other steps I should take? My wife is concerned because she thought this vehicle was a bad buy.

Anonymous 2018-02-09 14:10

I’ve already checked the ignition fuse in the rear fuse box — it’s good on both sides and shows proper continuity.

Anonymous 2018-02-09 14:28

Since I have 12V at fuse #47, does that confirm my ignition switch is functioning properly?

Anonymous 2018-02-09 16:06

If you have 12V at fuse 47 in the 'run' position, then your ignition switch is working correctly — it supplies power to the rear fuses. Next step: Clean the transmission connector and reconnect it. Clear the fault codes and test drive. If issues persist, refer to a transmission harness pinout diagram. The return signal from the transmission to the PCM must also be verified.

Anonymous 2018-02-09 16:23

Attached is a photo showing terminal E — I previously measured 12V at this point, but only when the fuse was live.

Anonymous 2018-02-09 17:35

I rechecked terminal E with a better multimeter and found no voltage. This confirms the issue lies downstream or in the transmission component itself.

Anonymous 2018-02-09 18:18

Is there anything else I should check? I didn’t realize the PCM sends 12V to the transmission — is that normal operation?

Anonymous 2018-02-10 08:32

The 12V flows from the solenoid *to* the PCM, not from the PCM. The PCM monitors this circuit for voltage changes when commanding functions like TCC (Torque Converter Clutch). If no 12V is detected at terminal E or in return circuits, the system will register a fault. In your case, the monitor isn’t detecting 12V — that’s why we’re checking if power reaches component terminals (E) and whether it returns from the transmission. This helps isolate whether the issue is wiring or internal.

Anonymous 2018-02-10 09:58

I just finished testing terminal E with a more accurate multimeter and now see 12V. I removed the transmission pan and inspected the solenoids — one of them (the passenger-side rear solenoid) has a grey end piece that came loose and appears burnt. Could this be the root cause? Would a cracked or broken internal component trigger all these codes?

Anonymous 2018-02-10 09:59

Thank you all for your help — I truly appreciate it!

Anonymous 2018-02-10 13:27

For reference: - P0740: Torque Converter Clutch Solenoid Circuit / Open - P0775: Shift Solenoid B Malfunction - P1810: TFP Valve Position Switch Circuit All these codes point to potential wiring or solenoid issues. I recommend using DeoxIT to clean connectors and ensure good electrical contact.

Anonymous 2018-02-11 09:47

I removed the transmission pan, inspected the plug, and tested with a different multimeter. All solenoids show 12V except one — it reads 11.9V. When I unplugged each solenoid, the passenger-side rear solenoid (on the back of the transmission) had its grey end piece fall off — it looked burnt. Could this internal failure be causing all these fault codes?

Anonymous 2018-02-11 09:50

Same as above: I removed the pan, checked the plug with a different meter. All solenoids show 12V except one (reading 11.9V). When unplugged, the passenger-side rear solenoid had its grey end piece detach — it appears burnt and damaged. Could this internal failure be responsible for all these fault codes?

Anonymous 2018-02-11 10:20

This is likely a straightforward fix: replace the faulty solenoid component. With limited access to diagrams and technical resources over the weekend, I believe all codes are related to wiring or solenoid failure. Next step: Inspect the wires from each solenoid to the transmission connector — this will help determine whether the issue is internal or in the harness.