Electrical problem when starting.

[McStash]

I have a 2006 Thomas Saf T Liner HDX. I'm starting my build out and now the bus won't start. I've got 12V, checked all the fuses I can find. Light and horn works. I turn the key and I get nothing. No dash lights no starting engagement nothing. Any ideas? It seams like it would be somthing simple. It started last year when I parked it.

 

[ewo1]

Is your bus a rear engine bus? If it is, have you checked the rear start switch?
Have you tried starting from the rear start switch?

what transmission do the bus have, is it the push pad type vs a lever?

 

[McStash]

Yes, it's a rear engine diesel Cat C7 with an Allison transmission l. I checked the rear switches. I haven't checked the power to the ignition switch yet, so maybe it's that.

Yes, it a push button engagement no lever.

 

[ewo1]

The reason i ask about the push buttons, do they light up when you turn the key to the on position?
If they do not, check the fuse for the TCM. If that fuse is blown or missing, the push pad will stay dark and when you turn the key, nothing happens. If for some reason one of those TCM wires got broken or ate by animals, you will get a no start issue.

I know, it happened to me!

 

[McStash]

The reason i ask about the push buttons, do they light up when you turn the key to the on position?
If they do not, check the fuse for the TCM. If that fuse is blown or missing, the push pad will stay dark and when you turn the key, nothing happens. If for some reason one of those TCM wires got broken or ate by animals, you will get a no start issue.

I know, it happened to me!

That sounds frustrating to diagnose. No, when I turn the key absolutly nothing happens. What is the TCM?

 

[turf]

you have a modern fancy bus compared to mine. but when that happens to me, its a lock out.

make sure all doors are closed tight, hatches closed (or open), any sleeping child alarm, foot on the brake, and that your in neutral.

there may be other lock outs but those are the most common.

good luck

 

[ewo1]

Does "absolutely nothing happens" mean that when you turn the key the tranny selector push pad DOES NOT light up?

TCM is Transmission control Module or tranny computer in simple terms.

If the TCM is not getting power, push pad stays dark and bus WILL NOT start.

 

[BamaBus]

.

 

[ewo1]

you have a modern fancy bus compared to mine. but when that happens to me, its a lock out.

make sure all doors are closed tight, hatches closed (or open), any sleeping child alarm, foot on the brake, and that your in neutral.

there may be other lock outs but those are the most common.

good luck

Yes, this is a very good point! some busses, if the safety latches are not properly working bus may not start!

 

[ewo1]

I have a 2006 Thomas Saf T Liner HDX. I'm starting my build out and now the bus won't start. I've got 12V, checked all the fuses I can find. Light and horn works. I turn the key and I get nothing. No dash lights no starting engagement nothing. Any ideas? It seams like it would be somthing simple. It started last year when I parked it.

I forgot to ask the most obvious question, you started your buildout....did you cut, remove any wires or door latches anywhere in the bus?

 

[cessna175]

Good afternoon guys. Don't forget to check the ignition switch itself. They do wear out after a bunch of start cycles. They are easy to check with a good multimeter. Thru the years, I've changed quite a few on various older ground support equipment and trucks. Your start circuit will always be independent of the other electrical systems. they are usually easy to troubleshoot. good luck.

 

[BamaBus]

I have a 2006 Thomas Saf T Liner HDX. I'm starting my build out and now the bus won't start. I've got 12V, checked all the fuses I can find. Light and horn works. I turn the key and I get nothing. No dash lights no starting engagement nothing. Any ideas? It seams like it would be somthing simple. It started last year when I parked it.

Seems this is a recurring issue. You posted about it in '23 where you said it happened before. I suspect you have a power supply problem that cuts power but it never got resolved. I would start at the battery and follow the 12v to wherever it leads checking connections.

 

[FawnaFox]

Are all of your exit doors unlocked? Some busses can have ignition interlocks if the emergency exit doors are locked or not properly secured (Ask me how I know)

 

[ewo1]

Seems this is a recurring issue. You posted about it in '23 where you said it happened before. I suspect you have a power supply problem that cuts power but it never got resolved. I would start at the battery and follow the 12v to wherever it leads checking connections.

Yup....May 29, 2023 posted-> 2005 Thomas Saf-T-Liner dash light and no start

I turn the key and nothing happens, the headlights come on but outside of that it's dead. I had this problem once before and it was related to the safety switches. Unfortunately in the course of "jiggling" some.wires it randomly started to work. I never did find figure out the problem.
I'd like to bypass the safety system entirely so I don't have this problem again.

 

[Timeline]

Replacing the safety switch is not a big job on this Allison 2500. The part was not super expensive. Mine had a big handful of small rocks behind it which was funny to find there!

 

[Mr P]

Seems this is a recurring issue. You posted about it in '23 where you said it happened before. I suspect you have a power supply problem that cuts power but it never got resolved. I would start at the battery and follow the 12v to wherever it leads checking connections.

Confession time..... lol

Customers that tell me only a fraction of the story....don't do themselves any favors.

 

[LilBusDude]

Just putting an idea out there,

I've recentely took down the tranny of my 7.3 powerstroke and couldn't figure out why the starter would not even budge when i turned the key, until i realised the tranny command by the stearing wheel has to be properly adjusted, to properly push the tranny gear in park mode to allows any firing what so ever.

If that ever helps anyone one day

Cheers

 

[McStash]

Does "absolutely nothing happens" mean that when you turn the key the tranny selector push pad DOES NOT light up?

TCM is Transmission control Module or tranny computer in simple terms.

If the TCM is not getting power, push pad stays dark and bus WILL NOT start.

That's correct, absoluting nothing happens. I've been through the fuses and can't find anything. But, both the horn and lights work. It's not a lock out, I've had those.

 

[turf]

has your battery been disconnected? is it connected correctly?

my bus has 2 leads the the positive and a single lead to the negative. i've hooked them up wrong before and the bus ran but no dash power.

 

[McStash]

Unfortunately yes, they are hooked up correctly. Nothing's changed since it worked last. Voltage is 12.8 at the fuse box. I'm thinking I need to check my key assembly.