unretrievable diagnostic codes
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New User
Joined: Sep 2004
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unretrievable diagnostic codes
cant get pcm to flash codes on a 1993 f150 302. The check engine light is on and operateable. Definitely should get codes since i have a major problem. the check engine light comes on when ignition is turned on and does not go off engine running or not; selftest activated or not. Have used both the jumper method and the plug in with the test and hold switch. while trying to initiate the engine running test with the plug in type when i move the switch from hold to test the engine dies. truck has been running very rich fuel consumption is nearly doubled, have replaced distributor, map, icm, tbs, o2, fuel pressure regulator. I have replaced most of these items even though they passed the meter checks. have not been able to retrieve codes since problem started. Have recieved codes before from this truck. is it the pcm and what is the best way to check it with a meter. The reason i havnt tried to check it with meter is fear of damaging the pcm.
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New User
Joined: Sep 2004
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thanks for the reply
care was taken to insure a good connection between scan tool and the diagnostic and self test leads. i have also tried initiating self test as described in haynes manual with no success. the later method has been used with success in the past
Postmaster
Joined: Mar 2004
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From: Michigan
I have had a few come into the dealership that would not communicate period!But thats not surprising for a 11 year old pcm.But before I went into checking supply voltages,reference signals,etc,If it were mine I would go ahead and disconnect the battery wait ten min,and then reconnect and go for a ten mile ride.If the light comes back on,then I have a hard fault to address.Which you can do without replacing a pcm just because it wont communicate. but gets into more testing
Elder User
Joined: Jul 2004
Posts: 911
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From: Northern Virginia, USA
I'd fiddle with the thing just like King Triton says. unplug and re-plug every connector you can find under the hood (in addition to the self-test), one connector at a time, and physically inspect the wiring as well for shorts or breaks to eliminate the wiring harness as a problem. Then check for codes. If still nothing, get out your Multimeter and a Haynes/Chiltons and start checking harness voltages.
You said your engine stalls when you turn on the hand-tester. I think this is good. I accidentally left my self-test jumper installed and went to work one morning. Didn't get 100 feet before the thing ran terrible and died. Your PCM may not be [completely] bad. But I could be wrong.
Good luck!
You said your engine stalls when you turn on the hand-tester. I think this is good. I accidentally left my self-test jumper installed and went to work one morning. Didn't get 100 feet before the thing ran terrible and died. Your PCM may not be [completely] bad. But I could be wrong.
Good luck!
