Last week during a very muddy and late night evacuation of some 200 youth, I lost my reverse gear and then forward gears in 4 hi on an 01 LX. This was scary. All this at 3 am in the morning. At one point I had 13 people in the LX. We carried on in 4 Lo.
Other clues included my speedometer suddenly going from 0 to 120 and back and forth and some error codes P0715 and p1700.
P0715 and P1700 are about a bad signal coming from the transmission output shaft speed sensor.
Once daylight arrived and I made it out of the hills I climbed under the truck and found that the in-line speed sensor offset device I used to adjust the speedo for my 33s had two wires yanked out of the plug, so I removed it and plugged the sensor directly into the ECU. Reconnected the battery and had reverse and forward gears again in 4 Lo and 4 Hi. What a relief.
So here’s what I think:
When the ECU can’t measure the vehicle speed, or if the signal indicates a non-zero speed it won’t let the transmission engage reverse. You can put the lever in reverse but the transmission won’t go into reverse. The engine will rev but it stays in neutral or park.
Interestingly, if the output shaft sensor information is bad or not available the ECU will not allow forward gear engagement in 4 hi either. The engine won’t even rev up if you push the throttle. It just stays at idle. In 4 Lo it did work.
I am not sure how the wires got pulled out of the connector. It was a long night with a lot of slithery driving in very rutted roads. It’s quite possible that I did not leave enough play in the cables to handle enough flex and shift of the drive train, or I drove over something, or flinged some mud at it.
Either way I’m grateful that the fix was easy and post the experience to help any of you in the future. And maybe help me remember myself!
Plan is to fix the speed sensor adjuster cable and connector and replace it. I want to do it so the actual box and it’s buttons are accessible in the cab so I can adjust it more easily. Before you had to be under to adjust the real speed which seems like an unnecessary hassle. I’ll also protect the wires better with some more play.
Other clues included my speedometer suddenly going from 0 to 120 and back and forth and some error codes P0715 and p1700.
P0715 and P1700 are about a bad signal coming from the transmission output shaft speed sensor.
Once daylight arrived and I made it out of the hills I climbed under the truck and found that the in-line speed sensor offset device I used to adjust the speedo for my 33s had two wires yanked out of the plug, so I removed it and plugged the sensor directly into the ECU. Reconnected the battery and had reverse and forward gears again in 4 Lo and 4 Hi. What a relief.
So here’s what I think:
When the ECU can’t measure the vehicle speed, or if the signal indicates a non-zero speed it won’t let the transmission engage reverse. You can put the lever in reverse but the transmission won’t go into reverse. The engine will rev but it stays in neutral or park.
Interestingly, if the output shaft sensor information is bad or not available the ECU will not allow forward gear engagement in 4 hi either. The engine won’t even rev up if you push the throttle. It just stays at idle. In 4 Lo it did work.
I am not sure how the wires got pulled out of the connector. It was a long night with a lot of slithery driving in very rutted roads. It’s quite possible that I did not leave enough play in the cables to handle enough flex and shift of the drive train, or I drove over something, or flinged some mud at it.
Either way I’m grateful that the fix was easy and post the experience to help any of you in the future. And maybe help me remember myself!
Plan is to fix the speed sensor adjuster cable and connector and replace it. I want to do it so the actual box and it’s buttons are accessible in the cab so I can adjust it more easily. Before you had to be under to adjust the real speed which seems like an unnecessary hassle. I’ll also protect the wires better with some more play.
