M1088a1 disconnect switch relay problem

[Ronmar]

Did you ever bypass AND measure voltages? If the disconnect is bypassed, whether it clicks or not makes no difference.

I would bypass the disconnect module, and both the ignition relays at the same time. Things may start clicking but that is just a symptom of voltage loss. Start at the batteries and measure 12 and 24 to ground. Then measure at the disconnect terminal 12 and 24 to ground. Then at the LBCD and power panel. You are looking for where the voltage drops off along the path to the power panel.

With the disconnect and ign relayes jumpered you should have only about half volt drop from the batteries to the ign terminals in the power panel with only the ign on loads applied...

 

[abfisher1798]

Finally had a moment to work on this girl.
I swapped out the LBCD with a borrowed unit and that cured the incessant clicking. Now I have full and steady power to the cab, but the start button had no effect. I raised the cab and jumped the solenoid on the frame and it fired right up. Then I discovered the transmission keypad was not on. I had a borrowed unit on hand so I hooked it up and that worked. I drove it around the lot a few times and everything seems copacetic. I parked it and tried the start button and still no effect at all.
I'm getting a replacement LBCD. I want to test the TCM one more time before calling it.

Will need to look into the start issue now.

Thanks very much for everyone's help. Any guidance on the start problem is much appreciated.

 

[NDT]

The transmission keypad needs to be fully functioning with no start inhibit codes to allow the start circuit to operate.

 

[Ronmar]

What NDT said. The TCU powers K26 when in neutral. K26 powers K11 which provides the power to the starter switches… 15 PSI of oil pressure de-energizes K11 disabling the starter and putting the alternator online… so does taking the trans out of neutral…

 

[abfisher1798]

What NDT said. The TCU powers K26 when in neutral. K26 powers K11 which provides the power to the starter switches… 15 PSI of oil pressure de-energizes K11 disabling the starter and putting the alternator online… so does taking the trans out of neutral…

I recall a reading a post a while back that referenced the lights on the generator, one led above 14v and the other above 28v. With the engine running, both lights are flashing amber, alternating between the two. Please remind me what that signifies.

 

[abfisher1798]

Now the spare TCM failed. Something terrible is happening.

 

[Ronmar]

Yellow is low voltage. Green is normal and red is high voltage… time to break out the voltmeter…

 

[abfisher1798]

I swapped the PDP with a known good unit and still no start. I did notice K11 does not light up with the ignition on.

 

[NDT]

More alternator info.

 

[Ronmar]

I swapped the PDP with a known good unit and still no start. I did notice K11 does not light up with the ignition on.

Yep, no K11, no start…

 

[abfisher1798]

What NDT said. The TCU powers K26 when in neutral. K26 powers K11 which provides the power to the starter switches… 15 PSI of oil pressure de-energizes K11 disabling the starter and putting the alternator online… so does taking the trans out of neutral…

I have power to the TCU, and power to K26, but nothing at K11.
Where do I go from here?

 

[NDT]

What is going on with the transmission controller at this point? All lit up and no codes?

 

[coachgeo]

I have power to the TCU, and power to K26, but nothing at K11.
Where do I go from here?

K11 is a solenoid on the Power Distribution panel correct? if so.. how are you determining you have no power to K11?- by sound of it not clicking?? or did you measure voltage there?

 

[abfisher1798]

K11 is a solenoid on the Power Distribution panel correct? if so.. how are you determining you have no power to K11?- by sound of it not clicking?? or did you measure voltage there?

K11 on this PDP is the ALT EXCITE relay. Pin 30 shows 24v but for some reason it will not supply power to 87.
I jumped pin 30 to 87 and 87a and still no power to Alt Excite.

 

[Ronmar]

There are 2 parts to the K11 circuit. DC voltage applied by K26 and a path to ground provided by the oil pressure switch.

Do you have an oil pressure idiot light when you turn on the ignition switch? The same path to ground that allows K11 to energize is also provided to the oil light by the low oil pressure switch down by the starter…

 

[abfisher1798]

What is going on with the transmission controller at this point? All lit up and no codes?

Transmission controller light up as it should. Circuit breaker also tests fine.
FYI, I can start the truck by jumping the auxiliary relay on the frame, but not with the start button.
I’m watching the generator now. It flashed alternating amber for several minutes, now is alternating with green at 28v and amber at 12v.

 

[Ronmar]

K11 on this PDP is the ALT EXCITE relay. Pin 30 shows 24v but for some reason it will not supply power to 87.
I jumped pin 30 to 87 and 87a and still no power to Alt Excite.

I thought this was a starting problem?

 

[abfisher1798]

I thought this was a starting problem?

It started out as something else. After replacing the LBCD the “clicking” issue went away. I also discovered the TCU was bad and changed that. Now everything powers up as normal but no response from the start button.
I mentioned the generator in case that might be a factor.

 

[TomTime]

I had a similar problem with the starting my engine from the starter button in the cab. But, it would start by jumping the relay on the frame by the starter. I had cleaned and checked everything everyone suggested and what it said to check in the TM's. Still no start and no K11 lite.
@Ronmar (big thanks to him!) suggested to check the engine oil switch and I found that was the problem. I took the two pin plug off the oil switch and jumped the two pins and K11 lite up and the engine started from the cab. Bad oil switch.
Not sure that will be your problem, but it may be worth checking.
Tom.

 

[Ronmar]

As Tomtime mentioned, thats why i asked if you have an oil idiot light. K11 must energize to power the start circuit. But if you jumpered K11 pin 30 to 87 that should have powered the start circuit the same as K11 would… that is of course provided you have a valid circuit. Back to rule one with DC, voltage is not good till measured good under load… With K11 30-87 jumpered, what does the voltage measure at K11 pin 30 when you push the start button?