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 2006 c2 mbe-906 no start
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jr4wdman
Active Member

13 Posts

Posted - 04/11/2013 :  7:09:23 PM  Show Profile  Visit jr4wdman's Homepage  Reply with Quote
We have a 2006 c-2 with a MBE-906 that presented with a no crank one morning. I went out and checked it out, I could force it to crank but it won't start. It has a code 248-02 active.

We've tested powers and grounds to the VCU and PLD-MR, found some grounds a little rough and repaired them all test good now, same results.

We tested and replaced the J-1587 cable between the VCU and the PLD-MR.
No joy.

Tested pin drag, ok.

We swapped the VCU and PLD-MR from another bus, no joy. They both will run the engine in the other bus just fine.

We have tested for cam and crank signal, had cam but no crank. Replaced the crank sensor, now have both. Still presents with active 248-02 and no crank if not forced.

What are we missing? Everybody here has beat their heads on this bus with no results but headaches, scrapped knuckles and sore backs!

Bassman
Top Member

USA
514 Posts

Posted - 04/12/2013 :  03:58:36 AM  Show Profile  Reply with Quote
I had one that did that once and a smaller wire off the starter that fed the computer I think rubbed through on some insulation. It wasn't metal to metal, just rubbed through til it had no more strands.
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eddo
Senior Member

USA
91 Posts

Posted - 04/12/2013 :  09:57:16 AM  Show Profile  Reply with Quote
how are you forcing it? Remote starter button hooked right up to starter?

If so:
Are you getting power to the starter solonoid when attempting to crank?
I had a starter relay that I didn't even know my truck had go bad once. Mine is on an IH, though, but never even knew it existed til it went bad.

Also have you checked the wires at the Neutral Safety switch to make sure it's working? lol, is the truck in gear?
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Fastback
Top Member

992 Posts

Posted - 04/12/2013 :  12:34:18 PM  Show Profile  Reply with Quote
Also make sure that if equipped with a vandal lock system, that the back door is not locked or there is not a problem in that circuitry.
Our 2006 C2 occasionaly locks itself when the driver closes the emergency door during his pretrip. Just sayin

Why yes, the ORIGinal CHARGER is a Fastback

Edited by - Fastback on 04/12/2013 12:35:31 PM
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JustinB
Advanced Member

United States
490 Posts

Posted - 04/12/2013 :  1:45:57 PM  Show Profile  Reply with Quote
128/248/02 = "Proprietary data link from PLD to VCU data erratic"
Check there.
- Confirm ECU and VCU Power and Ground
- Confirm harness connectivity
- Make sure that the AMU is triggering the brake lights when the brake pedal is pushed down.

I may not know the answer but I can usually find who does.
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jr4wdman
Active Member

13 Posts

Posted - 04/13/2013 :  06:48:24 AM  Show Profile  Visit jr4wdman's Homepage  Reply with Quote
quote:
Originally posted by eddo

how are you forcing it? Remote starter button hooked right up to starter?

If so:
Are you getting power to the starter solonoid when attempting to crank?
I had a starter relay that I didn't even know my truck had go bad once. Mine is on an IH, though, but never even knew it existed til it went bad.

Also have you checked the wires at the Neutral Safety switch to make sure it's working? lol, is the truck in gear?



If we allow the vehicle to go through the key on self checks it usually will not crank.

Sometimes by turning the key switch to crank multiple times in a row it will crank. We have not identified a pattern for this.

We can also get it to crank by turning key switch to crank position right after turning the key on, before everything goes through it's self test.

I believe the simple answer to the above phenomenon is that the when going through the key on self checks the VCU realizes it doesn't have the right information from the PLD-NR and says I will not allow the engine to crank because the engine will not run even if I do allow the engine to crank.

When trying to crank with multiple key cycles to the crank position the VCU may be come confused and allow crank.

When going straight to crank, the VCU hasn't had time to query the PLD-MR so it allows crank. Those are just guesses.

The transmission does display neutral in Allison DOC and if shifted will show the new gear selection.
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Rooky_07
New Member

USA
1 Posts

Posted - 04/18/2013 :  07:27:49 AM  Show Profile  Send Rooky_07 a Yahoo! Message  Reply with Quote
Ok, I am a tech for jr4wdman, and upon trying to diagnose this issue we brought in this unit's sister unit, put the PLD-MR and VCU off of the problem unit onto a known no issue unit. I disconnected the MBE Proprietary CAN pins and examined the waveform. On the no issue unit, I have a large square wave pattern from both the PLD-MR and the VCU. On the problem unit, I have a good square wave from the VCU, but not the PLD-MR. Going directly to the disconnected pins at the PLD-MR 16-pin connector I have very little if any waveform. I have tested and confirmed power and ground at the PLD-MR, and performed volt drop tests on those circuits. Have also checked the ignition Input circuit. All tests have yielded no cause for concern. So the thought process became that the PLD-MR was our problem. So we swapped the PLD-MR and VCU into the no issue unit and THAT unit started and ran perfectly with no codes or problems. So now that would indicate an issue not pertaining to our modules. What else can I check that my lead us in the right direction??
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jr4wdman
Active Member

13 Posts

Posted - 04/23/2013 :  5:32:36 PM  Show Profile  Visit jr4wdman's Homepage  Reply with Quote
Ok, we have the fix. After volt testing and load testing the power and grounds to the PLD-MR 4 times it finally showed us low voltage, 8vdc for one of the battery wires to the PLD-MR.

A single power wire comes off a fuse at the PDM on the left fender, it enters the wiring harness which loops around torward the transmission then forward up to the PLD-MR, there is a splice about a 100cm from the PLD-MR connector where it splits and becomes two.

We ran a new, heavier wire with new terminals and the splice closer to the PLD-MR. Engine now starts and runs great, at least in the shop.

A review of the test procedures. Intial testing was volt meter on the front side if the pins, ok. Then did volt drop test on the front side of the pins with a 12 amp load, the ground side had slightly high readings. We went through the grounds and retested, ok.
We also front side tested the proprietary data link circuit with a load. The volt drop was a little high so we replaced the proprietary data link with j1939 cable we keep around and new terminals. Retested the j1939 for volt drop, ok.

I performed the intial testing.

After this still had the same issue so over several days two techs repeated these same tests, they also were able to remove the rear covers of the connectors at the PLD-MR and do back side testing with the PLD-MR in the circuit with the key on. Again during these tests all readings were ok. They did perform other testing on engine sensors to prove that we had signals from the cam and crank sensors.

After Mike made the above post I had him go back through the testing,
he discovered with the connector plugged into the PLD-MR, voltage at the back side appeared ok on both battery supply terminals. When he disconnected he found only 8 vdc on one of the two battery supply terminals.

Prior to this episode volt drop testing has always found the problem for me quickly and accurately.

Either we consitently failed to properly load and voltage drop the suspect PLD-MR battery supply terninal or we did not supply enough load for the volt drop to present. The ECM power supply fuse in the PDM is a 30 amp.

Which brings forward the question how much of a load must be applied to a circuit to preform and accurate volt drop test, 5%, 20%, 50%, 80%?

When performing a volt drop test I apply a load and connect the voltmeter to one side of the circuit (power or ground) at the area where I have connected the load and connect the other lead of the voltmeter to the battery (the same side of the circuit, either power or ground) and read the voltmeter with current flowing through the circuit to the load. I usualy try to apply as much load as I think the circuit can safely handle.

We loaded tested to 12 amps, just under 50%.

Any thoughts?
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Bassman
Top Member

USA
514 Posts

Posted - 04/24/2013 :  03:47:38 AM  Show Profile  Reply with Quote
A headlight bulb works just fine to load a circuit like that.
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