Jim Warman Posted March 5, 2008 Share Posted March 5, 2008 Two trucks in a row.... these codes (along with others) in memory. No ODDTCs... Clear codes and run KOER... nothing. Take it for a drive.... U0101 (lost comm with TCM) returns. One truck has running concerns (almost like a bad plug wire???) , the other none. PC/ED is pretty plain about this code (U0101)... replace PCM. Not being fond of replacing modules, can anyone think of an explanation either I or the PC/ED is missing? I could explain it away with NVH causing vibrations that affect the PCM internally.... bbbbuuuuttttttt??? Quote Link to comment Share on other sites More sharing options...
GregH Posted March 5, 2008 Share Posted March 5, 2008 Well, the bus between the PCM and the TCM is internal to the casing of the PCM. So, if there is an issue with that bus, the only repair would be to replace the PCM. However, that's not the answer we want. Ok, early build? Wiring harnesses are issues, of course. Intermittant VREF shorts to ground, too. Later trucks aren't as affected by VREF shorts, ie. they don't down the processor and cycle the CEL, WIF, and WTS lights on the dash. On your truck with the running problem, I would most certainly pursue that concern first. Keep the U-codes in the back of your mind, but don't fret them yet. Once you find the cause of the running issue, then the reason for the U-codes may become apparent. Finally, the other truck with no running concerns. What are you doing to it? Why did you connect the scan tool to it? Is it a required periodic inspection? Do the U-codes need to be fixed? Forgive me for being obtuse, but in the south we have no yearly emissions testing or similar EPA or DOT requirements. I'm unfamiliar with what you guys face in the north... Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted March 6, 2008 Author Share Posted March 6, 2008 Sorry, my oversight.... Truck number two had CEL on... P0470 (freeze frame shows it's a cold start, cold weather key on code - this is addressed in a reprogram). Quote Link to comment Share on other sites More sharing options...
mchan68 Posted March 6, 2008 Share Posted March 6, 2008 I have one 2005 E-series that keeps flagging P0470. Checked all three PIDs EBP, MAP and BARO @ KOEO, and all are well within .2 psi of each other. PC/ED pinpoint test says that DTC is set when signal return GY/RD is open. That circuit is spliced with five other sensors IIRC. There were no other DTCs in memory. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted March 6, 2008 Author Share Posted March 6, 2008 Mike.. check your freeze frame data. When it is cold, we are seeing P0470s set at first key on (RPM = 0, EOT = cold, runtime = 0... that sort of stuff). Moisture collects in the sensor and then freezes. Since water expands when it freezes, this can apply pressure on the EBP and the PCM sees a rationality problem... Not documented, but the current PCM reflashes keep the PCM from looking at EBP for a set amount of time when the engine is cold. I <think> it assumes KOEO EBP based on MAP and/or BARO... For the need to quote a TSB to get paid for a reflash, we note on the RO that the choice to reflash is from "hotline instructions on previous similar repairs...". Quote Link to comment Share on other sites More sharing options...
mchan68 Posted March 6, 2008 Share Posted March 6, 2008 The particular unit I'm referring to already had its latest calibration. I swapped in a new EBP temporarily and got the same reading at KOEO. Quote Link to comment Share on other sites More sharing options...
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