OBDI code reading problem

[Tlutz]

I have a code that is turning the check engine light on after I drive a few miles. It comes on after driving a constant speed and then letting off the throttle completely (say right before braking). It will stay on the rest of the ride. When I shut the car off and turn it back on it resets and is off. I tried to use the paper clip short method to blink the code but get nothing. Then I got a new OBDI and II reader but it says there is no communication even though the ignition is in the "ON" position.

Could my wiring be messed up between the port and the computer and how would I fix this?

Could this possilbly be a vacuum leak?

94 3.4 V6 with a slushbox

[ssms5411]

Re: OBDI code reading problem

Sounds like EGR, Vac. leak would make the car run bad so you would know if its a vac. leak. Sorry don't know alot about OBD I.

[Hib Halverson]

Re: OBDI code reading problem

95 F-cars were part of the early roll-out of OBDII that GM ran back then to validate the system.

It is possible that some late 94 F-cars were also part of that. If your car has a 16-pin, rather than a 12-pin, DLC then it's part of that program. It has partial OBDII capability and the ECM may not support flash-code diagnostics. If that's the case, you'd get no response with jumping DLC terminals with a paper clip.

In addition, if you are trying to read a DTC when the problem is not occurring, (ie: the light is off) the DTC will be a history rather than a current code and, as I recall, flash-code diagnostics will not display history codes.

I suspect, you're going to need a scan tester (rather than a "code reader") which supports OBD systems to read the code while it is occurring.

On the other hand, if the car has the 12-pin DLC, you're jumping the correct terminals and you get no response from the ECM, you have bigger problems than just the MIL coming on during decel. You need the FSM for it's diagnostic instructions in re: no MIL flashes.

[2.8 Bird]

Re: OBDI code reading problem

Sometimes the computer chip can go bad and give you a misreading. How's your car running?

[Tlutz]

Re: OBDI code reading problem

I had some real problems driving north to Mich yesterday with the car. The cat converter plugged up and the back pressure came out thru the EGR valve effectively melting anything around it. I took it to a good repair shop I know today to get it repaired. The cat was changed, EGR changed, new plugs and wires and it was still running badly and hesitating at takeoff. We put their Snap On reader on and found it had a bad MAP sensor as well. When replacing that we found the wire plug was missing and it was just jammed into the receptical. Overall, lots of parts changed, and a bill of just over $600 (actually not that bad for all that was done).