GEM problems - I think
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4wd Low
Joined: Jun 2021
Posts: 12
Likes: 1
GEM problems - I think
2008 F550 6.8 Auto
About 7 intermittent problems started all at once and tell me if I'm wrong but I think it's all related to the GEM. Just trying to narrow this down.
1. CEL B1S1 heater circuit malfunction P0135
2. CEL B1S2 heater circuit malfunction P0155
3. CEL Evap purge valve circuit malfunction P0443
4. A/C randomly blows hot and takes about 10 seconds for the fan to kick on sometimes after turning it off
5. died on me once when I engaged the PTO
6. reverse lights randomly flicker while driving AND when sitting completely still in park.
7. Idle hunts 300 or so rpm's when this starts to happen.
I recently started driving down rural dirt and old logging roads a lot for work and hit a REALLY rough 30 or so feet the other day.
About 15 minutes after that I noticed these intermittent problems. The CEL came on the next day. I cleared it but still comes back with all 3 codes.
It's never had any of these issues till then.
Could it be the GEM? I did have a little corrosion and water intrusion on it about a 1.5 years ago but it's been perfect since.
Thanks in advanced!
About 7 intermittent problems started all at once and tell me if I'm wrong but I think it's all related to the GEM. Just trying to narrow this down.
1. CEL B1S1 heater circuit malfunction P0135
2. CEL B1S2 heater circuit malfunction P0155
3. CEL Evap purge valve circuit malfunction P0443
4. A/C randomly blows hot and takes about 10 seconds for the fan to kick on sometimes after turning it off
5. died on me once when I engaged the PTO
6. reverse lights randomly flicker while driving AND when sitting completely still in park.
7. Idle hunts 300 or so rpm's when this starts to happen.
I recently started driving down rural dirt and old logging roads a lot for work and hit a REALLY rough 30 or so feet the other day.
About 15 minutes after that I noticed these intermittent problems. The CEL came on the next day. I cleared it but still comes back with all 3 codes.
It's never had any of these issues till then.
Could it be the GEM? I did have a little corrosion and water intrusion on it about a 1.5 years ago but it's been perfect since.
Thanks in advanced!
FTE Leadership Emeritus
Joined: Sep 2000
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From: Stephensville WI
Just above the parking brake pedal assembly there is an electrical connector. Sometimes this connector can work loose from the jarring it experiences when the parking brake is released. A lot of different and seemingly unrelated circuits go through that connector. I'm not sure if that is your issue, or even if a 2008 F-550;would have that connector, but checking it costs you no money and just a little time.
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4wd Low
Joined: Jun 2021
Posts: 12
Likes: 1
Just above the parking brake pedal assembly there is an electrical connector. Sometimes this connector can work loose from the jarring it experiences when the parking brake is released. A lot of different and seemingly unrelated circuits go through that connector. I'm not sure if that is your issue, or even if a 2008 F-550;would have that connector, but checking it costs you no money and just a little time.
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4wd Low
Joined: Jun 2021
Posts: 12
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What's the official name? BCM? Smart junction box?
I'm suspecting whatever the thing is that looks like a fuse box but has a circuit board is the problem.I previously had water and corrosion issues on it. I just don't know what all goes through there but I know hvac and reverse lights do. (or so I've read)
Do the evap and 02 heater circuits run through there?
I'm suspecting whatever the thing is that looks like a fuse box but has a circuit board is the problem.I previously had water and corrosion issues on it. I just don't know what all goes through there but I know hvac and reverse lights do. (or so I've read)
Do the evap and 02 heater circuits run through there?
Hotshot
Joined: Jan 2004
Posts: 19,763
Likes: 1,081
From: St Louis
Official name is the Smart Junction Box (SJB). A combination of the cabin fuse box plus the multi-function modules.
Since you indicated all of the problems started at the same time, have to look for anything common to all or most of the concerns. The O2 sensor heaters and the purge valve circuits do not go into or through or from the SJB so it's ruled out for not being common to the issues.
I'd be suspicious of a poor/intermittent power or ground connection for the PCM. The PCM is about the only common denominator for most of your symptoms. The HVAC blower concern is a bit of an odd one out, though. Maybe insufficient battery electrical power/ground to the truck?
Since you indicated all of the problems started at the same time, have to look for anything common to all or most of the concerns. The O2 sensor heaters and the purge valve circuits do not go into or through or from the SJB so it's ruled out for not being common to the issues.
I'd be suspicious of a poor/intermittent power or ground connection for the PCM. The PCM is about the only common denominator for most of your symptoms. The HVAC blower concern is a bit of an odd one out, though. Maybe insufficient battery electrical power/ground to the truck?
Thread Starter
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4wd Low
Joined: Jun 2021
Posts: 12
Likes: 1
Official name is the Smart Junction Box (SJB). A combination of the cabin fuse box plus the multi-function modules.
Since you indicated all of the problems started at the same time, have to look for anything common to all or most of the concerns. The O2 sensor heaters and the purge valve circuits do not go into or through or from the SJB so it's ruled out for not being common to the issues.
I'd be suspicious of a poor/intermittent power or ground connection for the PCM. The PCM is about the only common denominator for most of your symptoms. The HVAC blower concern is a bit of an odd one out, though. Maybe insufficient battery electrical power/ground to the truck?
Since you indicated all of the problems started at the same time, have to look for anything common to all or most of the concerns. The O2 sensor heaters and the purge valve circuits do not go into or through or from the SJB so it's ruled out for not being common to the issues.
I'd be suspicious of a poor/intermittent power or ground connection for the PCM. The PCM is about the only common denominator for most of your symptoms. The HVAC blower concern is a bit of an odd one out, though. Maybe insufficient battery electrical power/ground to the truck?
The alternator is about 5 months old and battery is a couple of years old. I wonder though...could AC ripple current cause this? I went through 4 reman alternators before I found one that wouldn't set random codes on my 06 escape last year. It was the weirdest thing and the parts guy didn't believe me so we started testing them. Right out the box they were failing for ac voltage on the testing machine in the back. No new alternators were available. finally got one that passed.
I cleaned all the grounds on the firewall next to the PCM and near the SJB today with a little sandpaper, Pulled all the connectors on the SJB and PCM to re-seat them and inspect, they all look clean. cleaned the battery terminals and little ring terminals at the posts.
I drove it about an hour and it did just fine. I checked codes a few times and nothing was pending. Then out of nowhere my backup camera started flickering on and off and the A/C compressor drops out for a few seconds blowing normal air. I immediately check for codes and I have the same ones above pending. The entire hour drive home it did this
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Hotshot
Joined: Jan 2004
Posts: 19,763
Likes: 1,081
From: St Louis
Then out of nowhere my backup camera started flickering on and off
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Joined: Dec 2019
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From: San Diego, CA
Just curious but did you ever inspect the wire bundle that goes down to the O2 sensors and trace it back up towards the PCM? Circuit malfunction codes makes me think there is an open wire or damage to that bundle.
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