Exhaust pressure control relay low

[CIverson]

Ok, so I decide to do the key on/off/on/off/on deal, and a code came up. P0477. I proceeded to look it up on the list in the FAQ and I get this:



P0477 Exhaust Pressure Control Relay Low



What could be causing this? It dosen't set a check engine light.



I have a 4" MBRP and a Pacbrake, could one of those be setting it?

 

[rbattelle]

CIverson,



Okay, according to the PDM:



P0477 - Low Voltage on the Engine Brake Driver



Set Condition: when the signal from the engine brake driver does not match the signal from the engine brake driver feedback.



Possible Causes:

-Wiring Harness

-Engine brake driver relay

-Fused B+ open

-Engine brake driver signal circuit open

-Intermittent condition (they all say this )

-Engine brake driver signal circuit shorted to battery negative

-ECM



There are a series of tests that can be run in an effort to diagnose this. I'll note a few good ones:



1. With the ignition on but engine off, actuate the exhaust brake switch. Can you hear the relay click?



2. Check the resistance between terminals 1 and 2 of the engine brake relay. Should be less than 100 Ohms.



3. Measure the resistance of the engine brake driver signal circuit between the relay connector and battery negative. Should be more than 100k.



It seems like most of this stuff centers around the brake relay (assuming it's not a bad ECM). You might just want to get a new relay, if they're cheap.

 

[CIverson]

Thanks for all the info!



I'll have to do a few of the checks you mentioned, First I'll try disconnecting the batteries and see if that makes it go away for good.



I'm wondering of my brake sticking would have set that? It did this about a month ago and stuck closed for about 30 seconds.



Then last week I blew the fuse on the power lead to the compressor also.

 

[mgonske]

I had the same code for several weeks, and it kept recurring when I'd clear it. I looked at the above troubleshooting steps in the diagnostics manual, but didn't have a chance to chase it, so I had the dealer (who installed the brake) do it when I had the truck in for 45,000 mile service. They found a loose wire on a connector, and fixed it. OTOH, they weren't able to duplicate or find a reason for my "fan clutch" code

 

[JNutter]

I had that code a couple months ago. I also had a problem with the brake not working when it was cold. The dealer found a bad activation switch (the one on the shift lever) after I educated them on what the brake was, how it worked and how to trouble shoot it. Gotta love dealers...

 

[mgonske]

Well, I checked codes again this morning after the PMCR set good old P0336, and P0477 and P0480 were back again.