Code 55 and 56 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-11-2008, 08:30 PM   #1
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Default Code 55 and 56

Got both of these today. Cleared them, and they came back. EGR solenoid 3 and Quad B fault. FSM says they are likely related, but I'm not likely to get a Tech 1 on it to verify. Can this be fixed by lubing up the EGR valve?
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Old 05-12-2008, 12:40 PM   #2
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Hmm, FSM says "Poor drivability" is a symptom of the code 55. Could this developing problem be what did me in at the track?
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Old 05-12-2008, 12:58 PM   #3
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You would have had to have had the code at the track (and a CEL).

Clean and lube. I do it a couple times a year. I've never seen a quad related to mine.
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Old 05-12-2008, 01:18 PM   #4
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The quad drivers are mini-relays in the PCM. The drivers are protected by mini circuit breakers. The quad driver code is usually from a fault with the drivers (PCM) themselves or the device the driver operates is drawing too much current. See how many ohms resistance solenoid 3 has.
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Old 05-12-2008, 01:45 PM   #5
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Quote:
Originally Posted by willwren
You would have had to have had the code at the track (and a CEL).

Clean and lube. I do it a couple times a year. I've never seen a quad related to mine.
The test conditions it has to meet before it sets the code are fairly specific. Maybe it was sticking at times outside of the test conditions.... I'm just reaching. The light came on yesterday after driving for an hour or so, then went away for the next hour of driving and came back, and was still on this morning.
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Old 05-12-2008, 02:44 PM   #6
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EGR doesn't run at WOT.
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Old 05-12-2008, 02:59 PM   #7
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Right. I was thinking it could be open when I've got it loaded up to 1500-1800 rpm waiting for green, and when I launched, it didn't shut as quickly as it should.
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Old 05-12-2008, 07:34 PM   #8
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I checked on the way home. The PCM does command EGR shaft #3 open when I'm preloading at 1500-1800. If it was sticking or slow, I'm pretty sure that would cause a bunch of knock counts.
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Old 05-12-2008, 10:33 PM   #9
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Does anyone else think my theory has merit?
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Old 05-13-2008, 12:07 AM   #10
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Yup.

So fix it already!
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