EEC-IV CM code 29 is this a current issue?
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4th Gear
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EEC-IV CM code 29 is this a current issue?
My first post on this board; thanks for reading.
I drive a 1993 F250 7.3 IDI non-turbo. I've been dealing with flashing OD light for a while now. At first it was happening every time I drove the truck, sometimes going into limp mode. Sometimes not. I checked the fuses and two were blown under the hood, Left trailer brake light and trailer running lights. I put in new fuses and seemed to fix the OD light. Couldn't get it to flash again until I hooked to a trailer and it came on as soon as I put it in drive.
I did a KOEO test and got 111 followed by 29. I know 29 is VSS, but what I don't understand is since it is a CM code, does this mean it is not an active problem, but something that has been fixed in the past? I've only had the truck 3 or 4 months so I don't have all the history.
Is it possible I need to do a KOER test with the OD light flashing to get the actual code?
I drive a 1993 F250 7.3 IDI non-turbo. I've been dealing with flashing OD light for a while now. At first it was happening every time I drove the truck, sometimes going into limp mode. Sometimes not. I checked the fuses and two were blown under the hood, Left trailer brake light and trailer running lights. I put in new fuses and seemed to fix the OD light. Couldn't get it to flash again until I hooked to a trailer and it came on as soon as I put it in drive.
I did a KOEO test and got 111 followed by 29. I know 29 is VSS, but what I don't understand is since it is a CM code, does this mean it is not an active problem, but something that has been fixed in the past? I've only had the truck 3 or 4 months so I don't have all the history.
Is it possible I need to do a KOER test with the OD light flashing to get the actual code?
Logistics Pro
Joined: Nov 2013
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From: Mojave, Ca
If it's in CM, then it's a problem that happened in the past, but if the OD light is flashing and it's shifting hard, then you just checked the code when it was working correctly.
VSS is your vehicle speed sensor and the computer is having trouble reading the speed signal from your instrument cluster (PSOM). It could be a failing VSS sensor, or a dirty connector, bad wiring, or a failing PSOM. You can use a ohm meter to check the resistance of your VSS sensor in the rear diff. If it ohms out good (800 ohms-1400 ohms), then don't replace it. It's probably better than any auto parts store replacement.
VSS is your vehicle speed sensor and the computer is having trouble reading the speed signal from your instrument cluster (PSOM). It could be a failing VSS sensor, or a dirty connector, bad wiring, or a failing PSOM. You can use a ohm meter to check the resistance of your VSS sensor in the rear diff. If it ohms out good (800 ohms-1400 ohms), then don't replace it. It's probably better than any auto parts store replacement.
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4th Gear
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Thanks for the reply, Prototype. That is kind of what I was thinking. Since posting, I've determined that this only happens while I'm towing. I tried repeatedly to get the OD light to come on without a trailer, but can't. But when I hook up to a trailer, it starts flashing as soon as I start moving forward. It happens whether or not the trailer lights are connected to the truck.
Edit: I forgot to add that the speedometer works fine. Seems to be accurate and doesn't jump around.
I'll update the thread after testing the VSS and PSOM.
Edit: I forgot to add that the speedometer works fine. Seems to be accurate and doesn't jump around.
I'll update the thread after testing the VSS and PSOM.
If it's in CM, then it's a problem that happened in the past, but if the OD light is flashing and it's shifting hard, then you just checked the code when it was working correctly.
VSS is your vehicle speed sensor and the computer is having trouble reading the speed signal from your instrument cluster (PSOM). It could be a failing VSS sensor, or a dirty connector, bad wiring, or a failing PSOM. You can use a ohm meter to check the resistance of your VSS sensor in the rear diff. If it ohms out good (800 ohms-1400 ohms), then don't replace it. It's probably better than any auto parts store replacement.
VSS is your vehicle speed sensor and the computer is having trouble reading the speed signal from your instrument cluster (PSOM). It could be a failing VSS sensor, or a dirty connector, bad wiring, or a failing PSOM. You can use a ohm meter to check the resistance of your VSS sensor in the rear diff. If it ohms out good (800 ohms-1400 ohms), then don't replace it. It's probably better than any auto parts store replacement.
Last edited by chipfew; Oct 18, 2022 at 09:05 AM. Reason: Forgot to add some information.
Logistics Pro
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From: Mojave, Ca
Oh. That's a good riddle. Only when hooked up to a trailer, whether or not the trailer lights are plugged in. And speedo works correctly.
does your cruise control work correctly when the trailer is connected?
Since your speedo works correctly, I happen to think the problem is between your speedo and the computer by the e-brake pedal. But I don't know why the trailer has anything to do with it except maybe frame flex.
does your cruise control work correctly when the trailer is connected?
Since your speedo works correctly, I happen to think the problem is between your speedo and the computer by the e-brake pedal. But I don't know why the trailer has anything to do with it except maybe frame flex.
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4th Gear
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I've never tried the cruise control, so not sure if it works. Will have to try it. I guess that's something else in the same circuit as the VSS?
I was kind of thinking the same thing. That it's between the speedo and the computer.
Thanks for the input.
I was kind of thinking the same thing. That it's between the speedo and the computer.
Thanks for the input.
Logistics Pro
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From: Mojave, Ca
Yes. The speedometer (PSOM), feeds conditioned speed signal to both the ECM and the cruise control. So if the cc doesn't work, you can assume the problem is in the wiring behind the PSOM, or the PSOM itself. Still doesn't explain why it only happens with the trailer attached.
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4th Gear
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Is it possible that I could have fixed the 29 code when I changed the two fuses (before I changed those fuses OD was flashing anytime I drove, even without a trailer, and now with the new fuses, it only happens with the trailer), and the trailer issue could be caused by something else that isn't showing up in the test? The 29 code is coming in the CM codes, so it may not be a current issue. Would the trailer running lights or turn signals cause a 29?
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Logistics Pro
Joined: Nov 2013
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From: Mojave, Ca
No. Fuse G and Fuse D are dedicated to the trailer lights. They don't share any circuits with the truck systems.
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