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Discussion Starter #1
truck is a 2004 with common rail 5.9

Cold in Ontario right now and no start condition unless plugged in.

Troubleshooting the Intake heater grid and found this:

1) getting 12v to relays
2) grounds to relays are not broken
3) Dash light shows grid is being powered
4) No relay "click" when Key On
5) jump power and ground from battery to each relay separately and heater grid gets 12v and gets hot
6) jumped both grids directly and both work
7) checked volts on signal wires to both relays from ECM and they only read 3.5v with key on. The power from the ECM cycles normally (as in voltage stays at 3.5 until dash light goes off and then voltage drops to zero), but it's not getting the 12v required.
8) BOTH relays are only getting 3.5 volts from PCM...identical voltage to both relays.

From what I can tell, the ECM controls each relay separately as each relay has it's own wire going to the ECM.

The relays should cycle alternately pre-start and while truck is initially running and until it reaches a certain temp at which time the gird stops heating all together. I believe no issues here.

Relays function fine and supply 12v to heater grids when relays given 12 volts via jump wires, so I'm ruling out relay issues.

Heater grids work fine when tested via jump wires, so ruling them out.

I'm thinking because I'm getting identical voltages on the wires to the relays from the ECM, that the problem is in the ECM, not the wires or anything else.

Tomorrow or the next day, I'll check voltage at the pins on the ECM that is supposed to send 12v to each relay.

Has anyone had ECM issues with air intake heater relay voltage before?

Anything to add or suggest?

Thanks!
 

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Discussion Starter #2
Well the heater is getting a steady 12vs now and not sure why it was reading 3.5 on several readings over 2 days.

But still starting issues so have started a new thread.

Thanks,

Ron
 
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