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Hello, New Here and I am reaching out due to an issue that has me stumped.

A few days ago I drove my truck on a 200 mile trip, it performed flawlessly as always. Got home and when I pull up to my driveway to back it in the engine stumbled like I did not push in the clutch (but it's an automatic 6 speed Allison) and quit. I have never had that happen before, I put it in park, turned the key and she started up again, I backed it in and when I hit the brake before putting it in park it stalled again. I went inside, grabbed a beer and came back out to look things over, I attempted to restart the engine, turned the key ....NOTHING! No Crank, No Start ,,,,,,, I do NOT get an Engine Check Light or a Wait to Start (Glow Plug) Light. I now have a "BRAKES REQUIRE SERVICE" in the information display. I have a constant ABS light. ALL gauges with the exception of the Battery Gauge are full left, as if they are dead, the engine was still hot but said it was cold, fuel gauge is on Empty and low fuel light are on but the tank is FULL. EVERYTHING else works, radio, AC Blower, lights ...... I attempted to hook up my TECH II scanner and I have no OBDII communication with anything! NO ECM, BCM, TCM, Glow Plug Controller or ABS. I do have B+ power at the port .....

Batteries are fully charged, starter is a new GM unit, I can jump the starter relay and spin the engine all day long ...... so it's NOT the starter or batteries, lets get that out of the way.

The ECM has a stock LLY tune, and to my knowledge the TCM is the factory original as it's still riveted in place. Except for brakes and batteries this truck is all original and has 236,000 miles on it. It's been well taken care of.

I spent Easter weekend checking ALL fuses, relays, I became very intimate with the wiring harness both under the hood as well as the transmission and ABS, looked at all of the places that commonly cause these issues. I have checked for correct voltages and grounds on the ECM, TCM and I plan to check the ABS module tomorrow. I pulled the left front tire and removed the inner fender panel ...no wiring issues found.

I need to get the communication resolved as it's preventing me from seeing any codes. My gut tells me the ECM is bad because I checked all wiring relating to the GM High speed and low speed lan, there is nothing there! The dash gauges are on that buss as well. Even though the ECM has all the signals and voltages/grounds it needs ... if it cannot see them it will not function ...... and a case can be made for the ECM being bad. I do get some basic functionality from the TCM, if you put the gear selector in manual and hit the gear UP and DOWN button you can the display moving between gears 1 thru 6, you get the PRNDM indicator on the gear selector and I believe that all comes from the TCM, so it is at least sending indications to the dash .......... I don't want to just start throwing high dollar parts at the truck without getting some thoughts on the matter first. I don't buys ECM's without some troubleshooting and rationalization first. I am fairly certain it's NOT a wire rub or other broken wire ...... but I will keep looking.

My question is what role does the ABS controller play in all this? Could one of the ECM's have failed and shorted the can buss to ground? I think the ABS light and Brakes message is because of a com issue with the ABS controller and ECM. I will unplug the ABS controller tomorrow and see if I get coms back to the ECM, guess I should do the same with the TCM ........I have this expensive scan tool but with out the OBD port working It's no good in this case.

I had someone tell me the ECM would NOT activate the RUN/START circuit unless the ABS controller was good ..... don't know if I believe that. I had someone tell me the TCM could cause this problem as the ECM does NOT know the transmission is in Neutral or Park so it does not allow a start/Run. I did jump the neutral /park switch on the tranny but the TCM would still report the actual state to the ECM. So is it an ECM? Sure looks that way ...................

Sorry to ramble ... just trying to be transparent and detailed.

Thanks for your time .. and thanks in advance.
 

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Welcome to DieselPlace

I would individually load test those batteries.
Voltage is only one aspect of battery health. A load test will determine battery cell health.
A bad cell can cause all sorts of electrical gremlins
 

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Discussion Starter #3
Welcome to DieselPlace

I would individually load test those batteries.
Voltage is only one aspect of battery health. A load test will determine battery cell health.
A bad cell can cause all sorts of electrical gremlins
Thanks for responding ...... I have a $1300 dollar load tester on my service truck ..... and they pass with flying colors! Both batteries less than 3 months old! Because I messed around with the ignition on for hours I also had a charger running to keep the batteries fresh ....... I am all about simple stuff first. Thank you and you aren't wrong!
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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Brother, let me first say that I'm very sorry for your troubles. I feel your pain and you're not going to like what I have to say. Be that as it may...


You have a short or a bad ground somewhere. I don't know what trouble that has caused, or rather the extent of the trouble that that has caused, but I am pretty certain about it. I realized that you have gone through and checked a lot of power and a few grounds, but there are several grounds that go to the engine alone. Somebody posted a schematic I think for a 2005 a few days ago. It should be close enough. I would advise you Ohm out every single ground on that truck. There are a couple weird ones on the engine block. Thank you for pulling the fender liner and checking the wiring. There's a gremlin in there somewhere. It could be a fusible link I think at this point, but who knows. If you can isolate what feeds the TCM versus the PCM/ECM, You may be able to neck it down. There should be some ECM diagnostics as well where you can jumper power to it and make sure that it feeds back correctly. There are also many diesel shops that use EFI live to program things. Some of them have bench test sets. Probably wouldn't cost you too much to send it to one of them and have them test your ECM instead of throwing a part at it. I'll do some digging into the electrics tomorrow as it's just about bedtime where I live right now. Sorry she let you down. They do it sometimes. But they're worth keeping :)
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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Step 1-4 of what you do when you can't do diagnostics with a computer :) and by datalink connector, they mean what we call the ODBII port.

CIRCUIT DESCRIPTION
The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following:

Scan tool power battery positive voltage at terminal 16

Scan tool power ground at terminal 4

Common signal ground at terminal 5

The scan tool will power up with the ignition OFF. Some modules however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.

TEST DESCRIPTION

Step 1 - Step 4


The number below refers to the step number on the diagnostic table.

If the battery positive voltage and ground circuits of the DLC are functioning properly, the malfunction must be due to the scan tool.



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