code 31
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Fleet Mechanic
Joined: Jan 2013
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code 31
1989 f250 4.9L manual trans. 170k miles ...
the only code i am getting is 31. it shows up during KOEO and CM displays. didn't do an engine running test.
the only symptoms i am getting are :
a) SLIGHTLY rough idle from a cold start, idles fine when warm.
b) engine blows blue on occasion ... there doesn't seem to be any pattern to this ... it can show at start-up, fully warmed, idling or revving. it can go away as suddenly as it appears and not show up again for the rest of the day. checked pcv valve and it is rattling freely.
not overly concerned about either symptom on this old work-horse, but would like to know what the code 31 is pointing to so that i can perhaps get rid of the CEL. engine starts easily, has decent power and never stalls.
the only code i am getting is 31. it shows up during KOEO and CM displays. didn't do an engine running test.
the only symptoms i am getting are :
a) SLIGHTLY rough idle from a cold start, idles fine when warm.
b) engine blows blue on occasion ... there doesn't seem to be any pattern to this ... it can show at start-up, fully warmed, idling or revving. it can go away as suddenly as it appears and not show up again for the rest of the day. checked pcv valve and it is rattling freely.
not overly concerned about either symptom on this old work-horse, but would like to know what the code 31 is pointing to so that i can perhaps get rid of the CEL. engine starts easily, has decent power and never stalls.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Code 31 KOEO: EVP circuit below minimum voltage of 0.24 volts.
Code 31 CM: EVP circuit has intermittently failed below minimum voltage of 0.24 volts.
Get a DVM then measure the EVP output. EVP= EGR Valve Position Sensor.
Common causes of Code 31 are faulty EVP sensor, open wiring, faulty EGR valve or weak EGR diaphragm spring.
Since the EGR valve slightly preloads the EVP sensor it's hard to nail down the root cause. I would start with a new EVP sensor if the existing one does not measure correctly.
Some EVP info: http://web.archive.org/web/201104301...tion.com/?p=35
Code 31 CM: EVP circuit has intermittently failed below minimum voltage of 0.24 volts.
Get a DVM then measure the EVP output. EVP= EGR Valve Position Sensor.
Common causes of Code 31 are faulty EVP sensor, open wiring, faulty EGR valve or weak EGR diaphragm spring.
Since the EGR valve slightly preloads the EVP sensor it's hard to nail down the root cause. I would start with a new EVP sensor if the existing one does not measure correctly.
Some EVP info: http://web.archive.org/web/201104301...tion.com/?p=35
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