WTEC III Fault Code D1-6600

[jtcawrse]

My 2001 M1088 backed into the shop at Overland Adventure Truck to get the habitat married to the chassis yesterday. Today it’s throwing code D1-6600. That seems to mean that the serial communication between the engine and transmission has been lost.

We are looking at the TMs to see what we can see.

Any quick suggestions on where to start?

 

[Suprman]

Drop the passenger kick panel see if one of the 3 connectors came loose or something simple. The keypad display is powered by the tcm if you have display then its connected.

 

[jtcawrse]

Drop the passenger kick panel see if one of the 3 connectors came loose or something simple. The keypad display is powered by the tcm if you have display then its connected.

Display is working as that’s how we got the fault code.


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[Suprman]

Yes. I looked the code up again. Could be a wire harness issue. Maybe no comm with tps. Thats in the engine bay black box with a cable over to the throttle assembly

 

[jtcawrse]

Yes. I looked the code up again. Could be a wire harness issue. Maybe no comm with tps. Thats in the engine bay black box with a cable over to the throttle assembly

Is the wire harness often a problem?
Should I have one on hand?
Is it easy to replace?
Do you have one for sale?

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[Suprman]

The wire harnesses are known to have issues. Old insulation cracks and falls off. 2001 truck should be an a1 3126 engine no tps sorry didnt see that before. It gets the info from the engine computer. Did you make sure the tcm connectors were well seated?

 

[jtcawrse]

Did you make sure the tcm connectors were well seated?

Yes, loom connectors are firmly connected.


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[Suprman]

And you have good voltage batt connections alt connections tight polarity box connections are good. Could be alot of things. No pinched wires when the habitat went on? Could be a tcm issue. Swap in a tcm from another truck.

 

[Mullaney]

Yes, loom connectors are firmly connected.


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.
With the batteries disconnected it might be worth a very light film of anti oxidation paste on the connectors - and then plug them in and out a dozen times or so might help if there is any corrosion in there. Just working to make an okay connection into a good connection.

Might be better done with a tooth brush and some electrical contact cleaner or anti-ox spray cleaner...

 

[Ronmar]

Yea could be something got bumped or accidentally stepped on. I would separate and inspect the connections at the transmission and at the ECU…

 

[jtcawrse]

Just tried a known working TCU… nope.

 

[jtcawrse]

Suggestions on where to buy a replacement wire harness?

We seem to have exhausted our options For other simple solutions.

 

[Ronmar]

Suggestions on where to buy a replacement wire harness?

We seem to have exhausted our options For other simple solutions.

You said that fault was for comms between transmission and engine. Have you checked the connections at the engine control unit? Is the inline filter module still installed at the ECU?

 

[jtcawrse]

Keith, an Allison mechanic, just took a look.

The transmission seems to be fine. What he believes is the problem is an inter-lock communication. What I gathered from our conversation is that this is the chassis telling the transmission that the brakes are either applied or not applied. This is preventing the transmission from changing into a gear.

Another symptom that was noticed, the high idle worked before it went into the shop and now does not work.

 

[Ronmar]

Keith, an Allison mechanic, just took a look.

The transmission seems to be fine. What he believes is the problem is an inter-lock communication. What I gathered from our conversation is that this is the chassis telling the transmission that the brakes are either applied or not applied. This is preventing the transmission from changing into a gear.

Another symptom that was noticed, the high idle worked before it went into the shop and now does not work.

And both those symptoms point toward the ECU connection on the side of the engine… the service brake switch sends a signal to the ECU on the side of the engine, which puts that information out onto the data bus(Not sure if the trans uses brake info though). The high idle command switch feeds directly to the ECU. So again, have you checked the ECU connections?

 

[Vovka]

Hi im new to this forum and been reading a lot about trucks like mine and need help . I have a similar problem 1998 LMTV m1078 3116 pulling a code d1-6600 d2-4212 d3-6927 I found wires that where rubbing against steering wheel bar. I did try to fix that issue But still can’t get my truck to drive won’t go into gear no communication to Transmission so I thought I did a poorly job crimping my wires and tape. Would that problem burn my ECU ? Also noticed that my k34 relay gets to hot by touching it, ECU was on the worm end by touching it is that normal? Also I changed my A solenoid and internal wire harness in transmission , I check my grounds to Frame and polarity protection device I had 12v and 24v and I have 12v and 24v at PDP. now is it normal for duel voltage regular light jump from 12v to 24v back and forth? Thanks

 

[coachgeo]

Hi im new to this forum and been reading a lot about trucks like mine and need help . ...

congrats on your purchase and welcome aboard.

While am not a Moderator here...... I play one on TV (you got to be old to get that). Anyway.... kinda bad ju ju to pop in a post that can Hijack someone else's thread.... Now if it was an old thread....... with similar issues..... jumpinng in would be more than fine, would actually be good ju ju.. but since the OP is still seeking answers/advice....... not so good an idea IMHO.

Consider starting your own thread on your trucks issues??????

PS- actually this is not a very similar situation.... Original poster's engine is computerized...... (3126 or C7) your's; is not engine computerized.... and has a Wtec II... so its issues are likely bit different in what the fault is...... though maybe similar conceptually.

 

[Skyhawk13205]

Keith, an Allison mechanic, just took a look.

The transmission seems to be fine. What he believes is the problem is an inter-lock communication. What I gathered from our conversation is that this is the chassis telling the transmission that the brakes are either applied or not applied. This is preventing the transmission from changing into a gear.

Another symptom that was noticed, the high idle worked before it went into the shop and now does not work.

The 3126 and C7 have an input for service brakes, per the wiring diagram the input to service brakes is hard wired to the sensor common. You can do a wiring check from pin 5 on your ECM p2 connector to 45 to see if you have continuity.

 

[Vovka]

Didn’t know Sorry about that will start a new thread.

 

[jtcawrse]

The 3126 and C7 have an input for service brakes, per the wiring diagram the input to service brakes is hard wired to the sensor common. You can do a wiring check from pin 5 on your ECM p2 connector to 45 to see if you have continuity.

I’ll pass that on. Thank you! Still waiting… it must be a simple solution. It worked going in.


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