My 2001 ram 2500 just stopped displaying the “wait to start” light . Stinky cranks over fine but won’t fire. Would bad relays cause the light to stop working or is there something else I should be looking for? I am new to diesel but not mechanically daft and I do have a big book of words to reference in the Haynes category but didn’t find much in it helpful initially

 

Wait to Start light is driven the the ECM.... Relays are not involved. There are two relays for the grid heater, relays get power via fusible links from the battery. Verify you are getting power at pin 30 on both relays. Should be hot at all times.

 

The relays for the grid heater are controlled by the ECM as well. No light and no start could mean ECM not working, or the ECM "thinks" there is no need for the grid heater to come on. If you have a OBD2 reader/scanner see if the ECM is alive, and if it is check the coolant and air intake temperature readings. They should be ambient temperature.

 

At what temperature you are trying to start the engine? I've started my 12 valve at -5°C w/o grid heater with no issues.

 

I think you may have pointed me in a direction, my obd computer didn’t even recognize that it had been plugged into something. Is that the computer on the firewall behind the air box or do I need to look for another one?

 

The diesel is a bit convoluted, it has a PCM (powertrain control module) on the firewall that controls the transmission and instrument cluster etc. but there is also a ECM (engine control module) that is mounted to engine block. The OBD port is handled by the PCM so start there with the basics, power and ground connections. Check fuse 9 and 12 in the inside fuse panel and fuse 3 in the PDC.

 

I just got a “no bus” displayed in the odometer window so this may be as dumb as the capture bolt loosening itself at the fuse box.

 

"no bus" means the instrument cluster doesn't get any messages from the PCM, again pointing to the PCM having a problem.