Transmission issues with DTCs P0721 and P1794
Thread Starter
|
Registered User
Joined: Dec 2022
Posts: 1
Likes: 0
From: PNW WA State
Transmission issues with DTCs P0721 and P1794
Hi all, long time lurker and first time post. Over the weekend my truck developed a transmission issue out of nowhere and was causing issues with a hard shift from 1st to 2nd and going into limp mode in 4th gear.
Lots of surging and the truck trying to hunt for gears, excessive surging with RPMs going up to 4k RPM during shifts. I pulled out my scan tool and saw a pending P0721 output speed sensor range/performance code. Did a quick search and replaced said sensor on the rear driver side of the transmission. Cleared the code and it came back like the issue was not fixed at all, so I figured maybe the input speed sensor was faulty as well and replaced that and still had the same issue however I also now received a code for P0716 Input/Turbine Speed Sensor Circuit Range/Performance for the input sensor, a P0734 for gear ratio mismatch in 4th gear, a P1794 for speed sensor ground error and shortly after that a P0933 Hydraulic Pressure Sensor Range/Performance error.
I was at the end of my rope and close to bringing my truck to a dealership and have them figure it out but came across pinouts and pin descriptions to check for continuity and faults in the circuits with a multi meter to try and chase some electrical gremlins. I pulled my PCM connector closest to the engine and at the bottom of the connector I found condensation from the rain and cold weather we've been having in the PNW for the past few weeks. I sprayed the connections with some mass airflow cleaner (all I had on hand at the time, definitely should've used electrical connector cleaner) and took a heat gun and held it a good distance away as to not melt any connectors or plastic housings and after it seemed all dry I took some dielectric grease and applied it to the inside of each PCM connector.
After I took it for a test drive and still had some DTCs but the transmission shifted much better and didn't lock out but wasn't 100% normal and also got a P0933, P0732 for Gear 2 Incorrect Ratio and the P1794 DTC again, brought it back home and re-attached the PCM connectors and chased down the random DTCs (accidently forgot to replace a fuse M33 during troubleshooting) used my scan tool again to clear all DTCs and took another test drive. Lo and behold all issues were fixed, no pending DTCs and also took care of my random DTCs related to fuse M33. In fact my truck shifts and runs better than before. Just wanted to write this up as a potential solution to anyone having the same issue seeing as how there was very little if any information to the situation I was in and for a very cheap and quick fix before surrendering to the dealership or a mechanic.
TL;DR
Checked PCM Connections for condensation/corrosion, dried them out and applied dielectric grease and cleared codes and solved issues.
Lots of surging and the truck trying to hunt for gears, excessive surging with RPMs going up to 4k RPM during shifts. I pulled out my scan tool and saw a pending P0721 output speed sensor range/performance code. Did a quick search and replaced said sensor on the rear driver side of the transmission. Cleared the code and it came back like the issue was not fixed at all, so I figured maybe the input speed sensor was faulty as well and replaced that and still had the same issue however I also now received a code for P0716 Input/Turbine Speed Sensor Circuit Range/Performance for the input sensor, a P0734 for gear ratio mismatch in 4th gear, a P1794 for speed sensor ground error and shortly after that a P0933 Hydraulic Pressure Sensor Range/Performance error.
I was at the end of my rope and close to bringing my truck to a dealership and have them figure it out but came across pinouts and pin descriptions to check for continuity and faults in the circuits with a multi meter to try and chase some electrical gremlins. I pulled my PCM connector closest to the engine and at the bottom of the connector I found condensation from the rain and cold weather we've been having in the PNW for the past few weeks. I sprayed the connections with some mass airflow cleaner (all I had on hand at the time, definitely should've used electrical connector cleaner) and took a heat gun and held it a good distance away as to not melt any connectors or plastic housings and after it seemed all dry I took some dielectric grease and applied it to the inside of each PCM connector.
After I took it for a test drive and still had some DTCs but the transmission shifted much better and didn't lock out but wasn't 100% normal and also got a P0933, P0732 for Gear 2 Incorrect Ratio and the P1794 DTC again, brought it back home and re-attached the PCM connectors and chased down the random DTCs (accidently forgot to replace a fuse M33 during troubleshooting) used my scan tool again to clear all DTCs and took another test drive. Lo and behold all issues were fixed, no pending DTCs and also took care of my random DTCs related to fuse M33. In fact my truck shifts and runs better than before. Just wanted to write this up as a potential solution to anyone having the same issue seeing as how there was very little if any information to the situation I was in and for a very cheap and quick fix before surrendering to the dealership or a mechanic.
TL;DR
Checked PCM Connections for condensation/corrosion, dried them out and applied dielectric grease and cleared codes and solved issues.
Record Breaker
Joined: Jan 2004
Posts: 1,429
Likes: 192
From: United States
Our '12 had a similar issue although I don't remember the codes. I found a ground strap under the truck, kinda right hand side of the transmission tunnel that was in bad shape. IIRC it had been resting on the exhaust manifold. I replaced that and added some additional grounds for good measure.
I had also pulled the connector at the solenoid pack but couldn't spot anything at all. No dirt, no corrosion, no condensation, no bent pins. As such I reassembled without doing anything there.
So, perhaps just re-seating the connector fixed it, or my additional grounds fixed it.... but it never went into limp mode again. Has been several years now.
I had also pulled the connector at the solenoid pack but couldn't spot anything at all. No dirt, no corrosion, no condensation, no bent pins. As such I reassembled without doing anything there.
So, perhaps just re-seating the connector fixed it, or my additional grounds fixed it.... but it never went into limp mode again. Has been several years now.
