Ok so my grids no longer work. The "wait to start" light isn't coming on either. When I turn the key I'm getting a solid click that sounds like the relays tripping, but when I test voltage I'm getting battery voltage on one side, and about 0.13 volts on the other side of both relays. My first instinct is to replace the relays (I've heard about some non-cummins relays working better?) But reading up on here and seeing that the ECM might not be telling the grids to work. Just looking for a little feedback if I should start with the relays or look elsewhere.

 

The next test you can do will tell you if the ECM is actually trying to fire the relays. Put your test light between the two smaller control wires on either relay and turn the key on. If the relay coil is being fed power and ground, the test lamp should light. That would indicate that the relay is at fault. If the test light does not light, you will need to determine if it is the power or the ground that is missing from the circuit, then backtrack through the circuit to focus in on the fault.

 

Does the wait to start light flash for a second or so, as in lamp test?

If not, first thing to check is the lamp.
Then if not, the PCM isn't working properly.
If the relays were bad, the wait to start timer should work anyway.

If the WTS light flashes lamp test, and nothing else, another fault could be the intake air temp sensor. If the PCM thinks the engine is warm, it won't fire the heaters.

 

Awesome thanks I'll do this next time it's cold

 

Unless you live somewhere where it gets really cold (think 0*F or colder), You don't even really need the grids. Plenty of people running without them. I know that even way up north here, I disabled them from roughly March through Nov/Dec without any problems.

Just my .02...