Community Forums

deprived · 11-25-2020, 04:51 PM

I have a front-engine diesel, 2008 6.7 Cummins in a Freightliner chassis.

After consulting the shop manual, I was pretty sure I had located the starter relay (see photo). I disconnected one of small wires and the engine started right up, but I did get a CEL and a STOP dash light. I tried it again with the other wire disconnected and again, the engine started right up with a CEL that went out after a couple of seconds.

If this isn't the starter relay, what is it? And if it is the starter relay, why does the engine start anyway with either of the smaller wire disconnected?

A little puzzled here.

twinboat · 11-25-2020, 04:57 PM

Could be the preheat solenoid. They controls the intake air heaters.

deprived · 11-25-2020, 05:09 PM

Quote:

Originally Posted by twinboat

Could be the preheat solenoid. They controls the intake air heaters.

Could be! The heater could definitely pull some power. The large cables seem suited to high-draw applications like the starter motor and it even has a big fuse on it - I can't tell if it's 100a or 300a fuse because it has that orange anticorrosive paint on it.

Crasher · 11-25-2020, 07:40 PM

Where is it located? Is it the boost solenoid that connects the house batteries to the chassis batteries for a starting boost?

deprived · 11-25-2020, 08:05 PM

Quote:

Originally Posted by Crasher

Where is it located? Is it the boost solenoid that connects the house batteries to the chassis batteries for a starting boost?

It's up front in the engine area right next to the master cylinder. Boost solenoid would explain the big cables. Wow - I didn't even think of that. I'll check the manual

Still trying to figure out where the starter relay is.

deprived · 11-26-2020, 11:04 AM

Okay - that thing has got to be the starter relay. I found these technical renderings from Freightliner. Although if it is the starter relay, I still can't explain why I can start the vehicle with the relay activation wires disconnected.

deprived · 11-26-2020, 11:07 AM

And here's a picture of my setup. The routing of the cables is a little different than the diagrams.

twinboat · 11-26-2020, 11:59 AM

They don't normally fuse starter battery cables.

Crasher · 11-26-2020, 12:14 PM

Hook the wires back up. Then have someone go inside and press the booster switch while you have your hand on the solenoid. If you feel it click closed, you know what it is. If not, put a tester on the activation post to confirm there is voltage there when the button is pushed. If power is there and no click, you have a defective solenoid.