Hi, wacky problem here…

2002 camry se v6, 210k miles. Quit running. Cranks, just doesn’t start. I have 2 obd code readers, an older battery powered one and a newer ($25) one that powers off the obd port.

My older battery powered one doesn’t communicate with the car. Says “make sure key is on”. It has worked in the past. Either the scanner is dead, or something wacky in comms with the car.

The newer obd powered scanner works and successfully scans the ecu. No codes.

Now, here’s the wacky part: the car will start and run with the newer obd (obd port powered) scanner plugged in. Without the scanner plugged in, it won’t run.

The old battery powered scanner – no run.

Looked at this a little more, and found if I bridged pins 4 and 5 on the obd port (chassis ground and signal ground), it’ll start and run. Remove the bridge (a wire), and it doesn’t run.

Thoughts?

Thanks

 

Ok, first jumpered to put a good ground on pin 4 (obd chassis/body ground). No start.

Then jumpered to put good ground on pin 5 (obd signal ground). Starts and runs.

This points me towards something goofy with ECU, like ground isn’t so groundy.

Go poking around ECU, and notice that the ground wires (white with black stripe) are showing 7 volts with key in “on” position. That’s a mighty high voltage for a ground wire!

Then I put on a jumper and give one of those ground wires a good straight to battery ground. Car starts and runs.

We have definitely a bad ground here. Looking at wiring diagrams, and tracing wires, I see that the ECU ground wires (more than 1) get spliced together and get connected to a ground point in the rear of the engine compartment (bolts onto rear valve cover). I measure voltage there with key in “on”, 7 volts.

I unbolt the connection, clean it up, put it back together, and for giggles add another ground wire that I take over to a body ground point. Measure voltage and ECU ground wire with key in “on” position – a nice 0 volts. Go ahead and try to start car – starts and runs fine.

So that fixes the problem. And some other observations:

1-my older battery powered OBD scanner – it now works. With the ECU having a bad ground, its signal levels were not within spec that the scanner could probably read.

2-some other things that were giving me trouble over the last year seems to have been remediated as well. These I thought might be related, but didn’t want to make that full conclusion yet. But I think I can go there now. They are:


A-about a year ago my vehicle stability control starting going out, the VSC and TSC would come on intermittently, and eventually all the time. I had followed the procedure to recalibrate the yaw sensor, didn’t help. Figured maybe the yaw sensor had given up the ghost, and they’re kinda pricey so hadn’t worked on that yet….


B-about 6-8 months ago my coolant temp gauge started acting erratically, then eventually quit working. Replaced the sensor for grins ($20), no change. With OBD sensor I could see that coolant temp looked ok, so figured gauge dying (albeit that is rare).


C-about 2 months ago tach started acting erratically.

And now, no VSC or TSC light, coolant gauge working, tach working. I thinks bad ground may have been affecting them as well.