Hey guys,

I recently swapped a '95 LT1 & 4L60e into my '94 Camaro.

Car runs and drives great for the most part. It has 30# injectors, CC503, rebuilt transmission (Not sure what all is done to it), a 3400~ stall, and a 98+ 3.42 gear rear end.

The guy who is tuning my car did a basic flash to the PCM to recalibrate for the 30# injectors so I've been OK to drive it around town and get things finished up on it (alignment, exhaust hooked up, etc). I still have the v6 gauge cluster on it so my gauges are out of whack and the speedometer doesn't even attempt to move when I drive it around.

So here's the issue: When I come to stop at a light, the car does not downshift. Whatever gear I had it in when I came to a stop is the gear it takes off in when it starts driving. I also hooked FreeScan up to the OBD port and FreeScan does not show a speed rating.

Could it be that the VSS is bad or would it be the throttle position sensor? Or is it that it just needs the tune and recalibration before the PCM reads the data accurately? I do not believe I'm seeing any codes for it, but if either of them were bad would it throw a code? If so, what code would it throw up?

 

Definately get it tuned better. The PCM controls the shift point on the tranmission, and if its not getting the right rpm and speed, it most likely will not shift/run right.

 

Well I just got back from running DataMaster on it. It's throwing back DTC 24 and DTC 83... both VSS related. So I guess we know where to start. I just got my 1995 OEM Service Manuals off ebay and it says if the DTC 24 code is up then the PCM tells the transmission to default into 3rd gear. Seems to be a big chunk of my problems!

 

While DTC 24 for the VSS failure may have some affect on how the PCM handles the shifts per the shop manual, it shouldn't cause DTC 83, which is a fault in the TCC PWM solenoid circuit. You need to check the TCC circuit as well. Is it possible you have some wires crossed on the harness going back to the tranny?

 

Anythings possible, I guess. I'll check it out either way. The engine, transmission, harness, and PCM were all from the same vehicle and I didn't do much of any splicing on the engine harness to get it to work in the '94.

I'm not sure if it has anything to do with it, but I do remember seeing on Shbox's website C230 cavity J is "(Automatic) Park/neutral feed from transmission position switch (V8 VIN P only)" - being that I had a v6, C230-J is blank on the interior side. But, DataMaster showed when I shifted into P/N so it would seem the PCM still receives the signal regardless.

 

Is it possible that the VSS DTC codes that I'm getting is because I swapped a 3.42 rear end into the car? It's a 3 channel 98+ rear end and the PCM has not been reprogrammed yet for it.

 

The VSS has nothing to do with the rear axle assembly, rear axle ratio or the number of ABS/TCS channels. As long as the output shaft of the tranny is rotating, and the VSS is picking up the pulses from the reluctor gear, it should not trip the code for VSS failure. Doesn't matter whether its the right number of pulses per mile, or not. Put a frequency meter on the output wires from the VSS, and see if it is producing pulses as the output shaft turns. The 4l60E VSS reluctor ring should produce 40 pulses per tranny output shaft revolution.

 

But if the PCM is thinking that it's a 3.23 gear ratio and it's really a 3.42 and it's sending so X pulses and then you have the VSS in the transmission reading completely different pulses - wouldn't that make the PCM confused because it's expecting the speed sensor in the pumpkin to match the speed of the transmission according to the gear ratio that's programmed in the PCM?

I'm just trying to logically go through the items that don't require replacing parts first - I'm not the type of guy to start throwing new parts at everything and hoping it fixes it.

 

I'm not aware of any comparison of the rear axle ABS sensor output to the VSS output. The rear axle sensor is strictly for the ABS. The ABS does not connect to the PCM. Traction control interfaces with the PCM, but not ABS.

Example.... I was running 3.73 gears, and a T56 (17 pulses per output shaft rev). PCM was programmed accordingly. I swapped in a TH400 (40 pulses per output shaft rev) and a set of 4.11's. The PCM was left with the M6 tune (expecting 17 pulses/rev). Even though the speedo was reading more than twice the actual speed due to the pulse per rev mismatch, I did not get a code for the VSS.

Everything I have ever read about the VSS trouble code indicates it is based on checking the circuitry.

 

Well we figured out what it was - there was no continuity between the plug and the PCM for the yellow VSS wire - apparently somewhere in the harness it's broken/corroded away. We ran a new wire from the PCM to the plug and tada the car drove like a champ.


...atleast until the car died yesterday. Drained the oil and I've got a ton of gold flakes... so time to drop the whole engine back out.