Speedometer and Gas Gauge Problems
 

Hey Guys,
I recently got a 2002 ZR2 and I've got a couple problems I could use some insight on. I took it into a brake and muffler shop to connect something with the exhaust and cat converter that was being held together by a c-clamp and some pliers, as well as some brake issues. A couple brake lines were just replaced and after that I've had a problem with my speedometer not moving and my gas gauge twitching up and down. The check engine light is on and I was told that it was probably having to do with the O2 sensor, the previous owner stated they were getting a pre heat error when they tried to read the engine code, the brake shop stated their computer couldn't even read my computer. They also said there's a coolant leak so I'm replacing the water pump and radiator. I'm a little at loss where to start troubleshooting with the speedometer and gas gauge, would this most likely be the VSS or my main computer?

So those two gauges worked fine before the muffler and brake work was done?

Has more than one source said that your PCM will not interface with an ODBII code reader? Will the connector power on the ODBII reader?


George

Yes, those gauges were working fine before the muffler and brake shop.
And the shop said that their OBD reader wasn't able to communicate with my computer. Which is a little strange to me since the previous owner said that they were able to get a reading with their own scanner.

The wiring was probably disturbed. Reading the codes can help narrow this down. For instance the fuel tank pressure sender shares a ground with the fuel level sender but if there is no evap codes then it’s not that ground so we move on. You should get scanner capability and report if you can connect to the pcm. If not then we can test the connector power and ground.

George

I'll have to get a scanner and see what it's saying. I checked the battery cables and the shop must have replaced the bolt for the positive side because the one that was in there wasn't making enough contact with the terminal. After replacing that and taking off the boot, the speedometer works a little better but it still has trouble reading speeds under 30 mph and is slow to shift gears. The gas gauge is no longer twitching up and down though. Would you have any recommendations on which wiring might be mostly likely to cause this? I did also see that there was an electrical connector under the left front side towards the bottom that wasn't connected so I connected that. No idea what that was honestly, but I didn't notice a difference in anything after doing that.

The signal for the speedometer comes from the VSS which is located at the right rear of the transmission with two wires - ppl/wht and Lt Grn/Blk. On a 2WD that pair of wires goes to the PCM in the right front of the engine compartment. If its a 4WD then first they pass through connector C116 at the top rear of the transmission.

George

There are also grounded shield wires at each end. Near the transmission that shield goes from bare to black and attaches at G117 at the left rear engine compartment. At the PCM that is also bare to black and attached at G104 left rear of the cylinder head.

George