When I plug in a diagnostic tool made for my '89 and turn the ignition switch on, the service engine soon light stays on with no flashing. Please help, thank you.
I'm using the Actron CP9001 code scanner. The service soon light stays on constantly when the scanner is used and the range and MPG readings are working when driving.
The SES light should flash when you short pins A to B on the ALDL connector. The SES light will not flash when my scan device is attached to my 89 Vette. I cannot recall if the light is illuminated when the scan tool is attached.
I tried connecting terminal A and B, the ses light stayed on with no flashing. If the ses light had a short to ground I don't think it would light up at all. The ses light does go off when the engine is started. Does terminal B go directly to the ECM, if so should I run a ground wire at the ECM where terminal B connects?
Check Engine Light is powered by the Injector 1 Fuse. ECM drives or grounds the Light when a system fault is detected or it's put in Diagnostic Mode. It's put in Diagnostic Mode by grounding the Diagnostic Signal, Pin B at the link; Pin A9 at the ECM, a 5.5 volt reference. Ground path is to the Engine. You troubleshoot a short to ground by disconnecting the ECM. If the Light goes off, reconnect and jumper a 12 volt test light connected to ground to Pin A9 at the ECM. If that flashes a 12, the Diagnostic line to Pin B is open. If it doesn't, you probably need a new ECM.
When the engine was at operating temp the ses light did flash a #12 code constantly in diagnostic mode. When the engine cooled down the ses light stayed on constantly with no flashing in diagonostic mode. Should I still try the last procedure you suggested?
I'd run both tests because you seem to be saying that it won't provide serial data and there's a steady light. Engine temp doesn't matter - hot or cold it should flash a 12. The outlined tests are for this situation. It's either got a short to ground on the drive side; an open in the diagnostic signal or a funky ECM. The circuit is extemely simple.
If you want to see if it will spit out a trouble code, disconnect the TPS with it running and check for a 22 - though I'd verify the basic circuitry first.
I tried the test procedure you suggested, no flashing light. Which solenoids and relays should be checked for resistance before I replace the ECM? Can a defective prom chip inside the ECM also cause this problem?
There are no solenoids or relays involved. Yes, the Prom could be the problem, but it's more likely to be the ECM. Just be sure you jumpered the diagnostic at the ECM, Pin A9 and that someone was looking at the light as you usually have to lay upside down to access the ECM.
After removing the two plugs from the ECM and reconnecting the ses flashes a constant code 12 in diagnostic mode, but the radiator fan also comes on and stays on. Is it normal for the fan to come on during diagnostic mode? I'll probably end up replacing the two plugs going to the ECM eventually.
After removing the two plugs from the ECM and reconnecting the ses flashes a constant code 12 in diagnostic mode, but the radiator fan also comes on and stays on. Is it normal for the fan to come on during diagnostic mode? I'll probably end up replacing the two plugs going to the ECM eventually.
Jam04: Before you go and buy another ECM, I suggest you go to your local Auto Zone store and ask for this key:
This key is FREE and you insert it into the right two contact holes in the upper row of the ALDL connector. Turn on the ignition.....do not start the car......and see if the SES light will flash 1 2 1 2 1 2. Make sure you turn off the ignition before removing the ALDL key. Hope this is helpful.
Started to have the same problem with the ECM so I replaced with a rebuilt ($79)and now the car runs beautiful. This problem all started with a stall out while driving and intermittent idle problems. After replacing the ECM idle is 1200 rpm on cold starts and 550 rpm when the motor is hot with no stall problems.
Glad you fixed it but 550 rpms seems a bit low. If your scanner works, see what the target rpm is. Actual should be 50 +/- from target in drive. 100 +/- in neutral or park. Mine (Auto) usually targets 575 with 600 actual in Drive.
Hi I'm Dan.
I'm having the same problem with my 1988. I've done every diagnostic test and used three new computers and two new proms with the same result no flash and the car runs like crap. The car idles at 1500 rpm and when I put it in drive it stalls and shuts down. So, I went to a junkyard and picked up a ecm and prom from a 1988 chevy s-10 4 cyl and my light will flash. I'm at my wits end.
Corvette Store
89 no flashing light in diagnostic mode.
