rjex09

Hey guys, wondering if anyone has some insight into an issue I'm having. I've seen a couple threads describing similar issues, but couldn't find anything that matched exactly what my car was doing.

A few mornings back, I went out to start my 2000 C5 and got the dreaded reduced engine power message, coupled with "service traction control." It idled fine, just wouldn't rev past 2000 rpms. That was the first time I had ever seen either of those errors, so I grabbed my scanner, cleared the codes (which I will list), and everything was back to normal. I drove it that day with no further issues.

Went out the next morning, same thing happened. I cleared the codes again, and left for work. Sitting at a stop light, it popped the codes again. I pulled off the road and cleared them again with the intent of just getting the car back home and parking it. This time they wouldn't clear, they would instantly come back on. I got the car home in reduced power mode.

Here are the codes it set:
p1121
p1120
p1516

Luckily I have the 3 volume set of factory service manuals for it, so I've been reading up on those codes, and am leaning toward looking into issues with the TAC module? I haven't done a whole lot of diagnosis yet. I was hoping somebody would have experience with this problem that could save me some time poking around with a multimeter. Also, any thoughts on the 'service traction control' message? I'm thinking it was probably triggered by whatever other problem I'm having electronically with the engine, and will go away when I get that fixed... Any advice would be greatly appreciated!! Thanks!

TB04TJ

Check the wires underneath the battery for signs of damage. Rodents like to nest in this area.

ezrider4u2

If you were not the original owner, there may have also been damage previously due to battery acid or something like that on the cables. Also check the connections to the TB plug, I had similar instance afte service at stealership. They had somehow managed to unplug my TB connector and the MAF connection.

Break a leg, hope you find the issue and it's nothing major.

rjex09

Thanks for the input guys! I'll give this stuff a go and post my results. I actually just bought the car not too long ago, so I don't know much about it's history.

8VETTE7 - Thanks for the reminder, I had forgotten that the C5 had that feature! I'll grab the codes off of it tomorrow and let you know what I get. Thanks!

rjex09

Ok. Here are my latest findings... I'm leaning strongly toward a new TPS.

I hooked it up to a scan tool tonight, the throttle percentage reading was all over the place with the key on, engine off. I was getting 90% throttle on the scan tool without the engine running, and nothing touching the gas pedal. It kept fluctuating on its own, and playing with the gas pedal didn't seem to really introduce any reason into the readings.

I pulled the TPS and started checking wires. (hint for anyone else who tries to find a TPS for their 2000 C5: For whatever reason, all the parts stores I tried kept giving me the wrong TPS. I had to have them look up for a 1999, which then brought up the correct sensor. It's the 2 in one sensor with 6 wires.) Both the 5 volt references were good, obviously no reading on the signal pins, and it read .4k ohms between either of the ground pins, and the negative battery terminal. My buddy thought that was a little high on the ground resistance, but I couldn't find any specs. We have continuity anyways.

Then we tested the sensor itself. (Keeping in mind that it's the one sensor unit, which actually has 2 sensors inside of it.) We ran resistance between the 5v reference pin, and the ground pin for sensor 1. It read open circuit. Same reading when we moved the lead to the sensor 1 signal pin. As for the pins on the #2 sensor half, we got continuity with low resistance between reference and ground, and a fluctuating resistance reading from the reference to the signal pin as we moved the sensor around. So my conclusion is that the first sensor is dead, causing my issues. I will try to track one down tomorrow and let you know what happens.

Also, if you clear the codes with the key on engine off, the p1221 returns immediately and instantaneously throws it back into limp mode. The other codes don't come back until you start the engine. Another reason why I think the TPS is the issue.

Thanks for your input!

Amixamse

Not sure if you seen my p1518 thread, Im in engine reduced power mode with constant p1518 but mine won't even start. I have constant voltage to fuse 17, and voltage to each female connector on tps wires. Before she died for good, she developed a rough idle and no throttle response. I'm not about to start replacing parts just yet, and maybe you shouldn't have to either.

Check your ground on back of driver head and in front of starter. Also look up ignition switch fix by bill curlee. Also check harness wires on driver side back of the intake, sometimes the wire runs raw on a metal bracket and can throw codes. Our problems aren't exactly the same, but just tryin to help.

rjex09

Well I caved and took it into the dealership. I double checked the TPS the next morning, and got perfect readings on all pins. Long story short, the dealership tracked it right back to the TPS. I was informed by the mechanic that it is common for a TPS to pass a bench test and still be the cause of the problem. Not sure how that works, but they replaced it and the problem is gone! So for anybody else who has this problem, don't second guess yourself, replace the darn TPS.