Transmission Failure or electrical short? - 1995 Automatic
Thread Starter
Cruising
Joined: Aug 2017
Posts: 10
Likes: 2
From: New Rochelle New York
Transmission Failure or electrical short? - 1995 Automatic
So I was driving to work this morning in the rain, and the car started revving up without the tires slipping or increasing speed (at first I assumed there was tire slippage and was confused because the traction control light didn't come on). I finally realized that something odd was going on with the transmission, and by that time I had to pull over, the car wouldn't move at all - forward in any gear or reverse because it was not transferring any power to the wheels. No check engine light. No codes at all (checked after I had it towed home). No transmission fluid leak. When I checked the fluid, it was full and had good red color.
I know the 4L60E transmission in my 1995 automatic is electronically controlled, I'm thinking maybe water caused a short in the control lines? It was raining pretty hard and I rarely if ever drive it in the rain. Luckily the tow truck driver (it was a flatbed actually) was able to help me get it back in the garage. When it finally dries out I'll see if the problem goes away. Seems like a mechanical problem should have thrown a code or two. Anyone have a similar issue or contrary view? I looked through the FSM and didn't see anything helpful. It was basically acting like it was always in neutral once I stopped .. no power to the wheels at all. I'm not that familiar with how it all works, but it seems like maybe one of the servos was on when it shouldn't have been.
I know the 4L60E transmission in my 1995 automatic is electronically controlled, I'm thinking maybe water caused a short in the control lines? It was raining pretty hard and I rarely if ever drive it in the rain. Luckily the tow truck driver (it was a flatbed actually) was able to help me get it back in the garage. When it finally dries out I'll see if the problem goes away. Seems like a mechanical problem should have thrown a code or two. Anyone have a similar issue or contrary view? I looked through the FSM and didn't see anything helpful. It was basically acting like it was always in neutral once I stopped .. no power to the wheels at all. I'm not that familiar with how it all works, but it seems like maybe one of the servos was on when it shouldn't have been.
Drifting
Joined: Apr 2020
Posts: 1,925
Likes: 610
From: Orange, CA
Agreed with Kevova. If it was just freerevving, that's likely going to be one of the clutches having gone dead. The '95 and up 4L60E does have a known failure point related to the torque converter clutch, but I do not believe this failure will impact normal drivability even if it were to completely fail.
Mechanical problems will not throw any codes. The car has no way of knowing that a mechanical component has failed. This is true for everything on the car--engine, transmission, brakes, etc. The only thing it can throw codes for are electronic components with feedback loops. So no codes, again, points to a hardware failure within the transmission.
When you go to test, see if manually shifting the transmission allows the car to move in any direction.
Mechanical problems will not throw any codes. The car has no way of knowing that a mechanical component has failed. This is true for everything on the car--engine, transmission, brakes, etc. The only thing it can throw codes for are electronic components with feedback loops. So no codes, again, points to a hardware failure within the transmission.
When you go to test, see if manually shifting the transmission allows the car to move in any direction.
Drifting
Joined: Apr 2020
Posts: 1,925
Likes: 610
From: Orange, CA
Check the fluid level.
Pull codes with the paperclip method. (Yes a 95 has an OBD II connector, but most codes are still OBD I and will display on the Check Engine Light.) Transmission codes do not illuminate the CEL, but they store in memory.
Because there is no Reverse as well as no forward gears, the issue is something that affects the entire transmission not just certain elements. Pump, fluid level, pressure control come to mind. A Line Pressure check with a mechanical gauge on the pressure tap on the driver side forward case will give hints to pump and pressure health. With the engine idling the pressure should be 80-ish psi. I use a separate TPS sensor, plug it into the harness and manipulate it with a screwdriver. At 100% TPS in P/N the pressure should approach 200psi. In Reverse, 100% TPS, pressure should be 250-275 psi. (These numbers are appx, from memory, but close enough for diagnosis. The FSM has specific test procedures and pressures).
Check the VALET fuse. This fuse is the source for power to the transmission. If VALET is blown, the transmission will be in 3rd gear only, but Reverse will not be affected.
Pull codes with the paperclip method. (Yes a 95 has an OBD II connector, but most codes are still OBD I and will display on the Check Engine Light.) Transmission codes do not illuminate the CEL, but they store in memory.
Because there is no Reverse as well as no forward gears, the issue is something that affects the entire transmission not just certain elements. Pump, fluid level, pressure control come to mind. A Line Pressure check with a mechanical gauge on the pressure tap on the driver side forward case will give hints to pump and pressure health. With the engine idling the pressure should be 80-ish psi. I use a separate TPS sensor, plug it into the harness and manipulate it with a screwdriver. At 100% TPS in P/N the pressure should approach 200psi. In Reverse, 100% TPS, pressure should be 250-275 psi. (These numbers are appx, from memory, but close enough for diagnosis. The FSM has specific test procedures and pressures).
Check the VALET fuse. This fuse is the source for power to the transmission. If VALET is blown, the transmission will be in 3rd gear only, but Reverse will not be affected.
And just a clarification--the 94-95 Corvette have an OBDII-shaped connector but all their operation is OBDI (8192 ALDL). OBDII was not until 1996. Plugging an OBDII reader into a '95 will not work. Your point about the paperclip method is accurate, however. For more information on how to do the paperclip method: https://tech.corvettecentral.com/201...trouble-codes/
Reverse uses 2 different clutches than any of the Forward gears do. So more than "one" clutch is not holding. The clutches involved would be the Reverse Input (this clutch NEVER fails), or Forward clutch (this can burn up from low line, or a cracked accumulator piston, but never fails on its own. I've seen forward clutch frictions from 100k + miles units where the writing on the surface is still legible.) Loss of BOTH forward and reverse is not "clutches". Probably not electronic either, unless it is Line pressure related.
The ECM supplies the "power" for the PCS, with the PCS disconnected, Line goes full high. About 200psi in P, N, or Forward gears. In a 95 the ECM is under the hood, and with a FSM the correct wire for the PCS would be easy to identify and de-pin for testing.
The ECM supplies the "power" for the PCS, with the PCS disconnected, Line goes full high. About 200psi in P, N, or Forward gears. In a 95 the ECM is under the hood, and with a FSM the correct wire for the PCS would be easy to identify and de-pin for testing.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
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From: near the thumb in the mitten
After rereading real red fluid; how long ago was fluid changed? If recent filter could have fell out of case. Causing no fluid to reach pump. Most mechanical parts normally make noise prior to failing. Broken input / turbine shaft would not.
Thread Starter
Cruising
Joined: Aug 2017
Posts: 10
Likes: 2
From: New Rochelle New York
To close out this post, the answer to the question was obviously transmission failure. I picked up the car this morning (after dropping it off at the transmission shop two days ago) and the mechanic told me that it looked like it blew up inside. He has a good rep in the area and hopefully it will last a long time now that it has been rebuilt.
