Soliciting help if anyone has any ideas. Ive got a "new to me" E38 PCM that I've wired into an RX7 swap with a custom tucked and wrapped harness. Everything is currently working, with the exception of the coolant sensor which per HPTuners is maxing at 305* and throwing code P0117. I've already tried swapping to a brand new coolant temp sensor, so I doubt thats the problem.

I checked the coolant temp connector in the engine bay and found that neither side of it had +5v like I was reading should be the case. Hmm, perhaps I hooked up the wiring incorrectly?

When I started digging in I found that on the gray connector on pins 21, 22 is where the coolant sensor hooks up to the PCM.

21 0.5 YE 410 ECT Sensor Signal - ECT Pin B
22 0.5 TN 2761 Low Reference - ECT Pin A

I tested continuity from the connector to the PCM gray connector, and its for sure those wires.

Next thought, perhaps I ground out a wire or something somewhere, So I ended up cutting the wires coming off of the PCM right near the PCM and ran 2 rogue wires across the engine bay and hooked up to the brand new coolant temp sensor. Still reading 305* in hp tuners. Argh...

Last thing, tried unhooking the rogue wires for the coolant sensor, and have literally NOTHING hooked up to Pins 21,22 for ECT. Turn the key forward, reading only .1V from either pin. Im under the impression it should be +5v and GND for each.

Any thoughts? I'm left with two thoughts, which is
1. Bad PCM, buy a new one and see.
2. Something goofy in the tune or how I've got the rest of the PCM wired thats causing it to not output +5v. (anyone have any ideas there? The rest of the outputs seem just fine, the engine will start, run, etc. No codes beyond the P0117 and coolant temp being pegged at 305*)

Help?

Much appreciation!

 

Not sure what the problem could be besides a bad PCM, very easy/cheap to swap and check... I bought one on eBay for my 2007 Yukon Denali and it came pre-programmed (for the wrong vehicle lol) so they sent me a replacement. Bottom line, I have 2 extra e38 ECUs sitting around if you need a new one. Do you have the ability to program them or you need it programmed?

 

Dang, I was thinking it was that. I've got hp tuners so can program but don't have licensing to swap os. Sounds like another pcm and more hp tuner licenses in my future!

 

if its just a bad 5v feed, maybe use a different one? there's bound to be a spare from egr, fuel level yadda yadda

 

 

Oh really! I was assuming the 5V was what feed the coolant sensor signal. So its actually "how much does the ground see" then? I'll give that a try tonight. Thanks!

 

Anyone know which one should be 5V? I'm assuming its "ECT Sensor Signal" on Pin B, not "Low ref" on Pin A?

21 0.5 YE 410 ECT Sensor Signal - ECT Pin B
22 0.5 TN 2761 Low Reference - ECT Pin A

 

Low Reference should be 5v, Sensor Signal should vary with temp to provide the reading...