Vehicle Speed Sensor Questions

[azu]

Speedometer suddenly went haywire and then reads zero. Transmission does not shift out of 1st gear. I scanned codes and got P0502 (Speed sensor circuit low) and an odd one, P0705 (Transaxle Range sensor/switch circuit malfunction). Probably needs a new VSS but my question is:

1) Are the two codes related or separate?

2) How difficult is replacing the sensor? I can see it from the engine compartment and looks pretty easy, disconnect wiring, one bolt.

[alec_b]

Sounds more like a tranny wiring issue. The range sensor is on top of the tranny kind of under the brake booster area, check the connections there. The other one, yea probably a VSS.

I find it a little odd that it happened at the same time, however.

[azu]

The range sensor is on top of the tranny kind of under the brake booster area, check the connections there.
I find it a little odd that it happened at the same time, however.

I agree it is odd. Daughter was on highway and speedo acted up and when getting off highway car stalled out. Restarted fine but tranny would not go out of 1st. Thanks for letting me know where the range sensor is, I had no idea.

P.S.

The range sensor code was the first one thrown followed by two VSS low circuit codes according to the scanner.

[alec_b]

Well a quick search of identifix is looking more and more like a PCM issue than a transmission component issue. The stall is also odd.

I had a chevy lumina in not too long ago that was acting very odd, ran extremely rich at times, hard hot start, and an occasional loss of speedometer. Turns out all 3 were related to a failing PCM. The conditions were all intermittent, also.

Check all the connections at the range sensor, vss, and PCM and see what happens.

[azu]

I have a spare PCM so I can swap and see if that is the problem or not. I won't be able to work on it until this weekend but I'll check all the connections. I did drive it yesterday after I cleared the codes. It did shift out of 1st in the parking lot but once it warmed up and I took it on the road it would not go past 1st gear and no speedo. No codes reappeared.

[azu]

Swapped PCM and same problem. I did get codes real quick though which was P0502. PCM ruled out.

I change VSS and same problem and code. The old VSS looked to be a newer one not original but I could be wrong. So it is not the VSS.

Is there anything internal where the VSS goes that could cause this problem?

I believe the problem is a wiring issue. Anyone have a diagram of the wiring harness that goes to the VSS?

[sandrock]

The VSS is directly wired to the PCM, and the only break in the wiring should be at the connector (firewall). VSS wiring will be twisted to keep stray signals from messing up the true speed signal as well.

An easy way to check for a break in the wiring is to take the connector off of the sensor. Next, install a jumper in that terminal to bridge those two wires. Go the PCM side of things, remove the connector associated with the VSS ( I dont have that connector info handy...someone else might chime in with that I hope), and check for continuity between the VSS hi and the VSS low wires. If you have continuity, the wiring is good, so put it all back. If it isn't there is a break in the wires somewhere.

THe other code deals with your neutral safety switch on the transmission. These are known to go bad as there are several circuits on that same switch, the range decoder being the one that goes out the most. If it throws a code, the PCM defaults to "D4" mode...it has no way of knowing (PCM-wise) if it's in park, neutral, or in gear, so it goes to the mode that allows it to operate as much as possible.

Your two issues are totally unrelated. In fact, the range switch code is one that doesn't throw a check-engine light, so you may have had that code for quite some time.

[azu]

break in the wiring should be at the connector (firewall).

This would be the connector that goes into the VSS, correct? That area the wires look bad.

[sandrock]

No. Firewall connector is the only place where the wiring breaks, so it can pass through the firewall.

The VSS connector might very well be oil soaked since its right there by the oil sending unit. Clean it with contact cleaner (both the connector and the sensor) and see what happens.

[azu]

It was a complete break in a wire about 2 inches from the connector. My daughter will be taking to local mechanic this week to have that done and what I believe is a leaky oil pressure sensor. My next house will have a lift or I'll have one installed . I just can't get to it underneath! Thanks everyone!!!!

[azu]

Back on the road!!


It was the wiring. From the oil leaking and heat it just deteriorated the wire until it broke. Took a while as daughter was paying this time! Local mechanic fixed for $85.