Heater Grid Relay .....PCM?

[B KIRK]

My #1 intake heater grid relay is staying on. It's enough of a draw to make my check engine light come on and give me a #47 code, (voltage to low). Relay is not sticking, it is getting a signal from PCM to run. Checked my intake air temp sensor and it looked clean as new. Can switch wires to both relays, and #1 circut will close that one it's on. I have a workshop manual, and it shows the PCM operating the relays buy sending out a ground. I checked the # 1 circut to make sure it was not grounding out elsewhere. Pulled connection at PCM, cleaned it, put some dielectric grease on it, and checked again. Same thing. Even cut wire next to PCM and still get a ground signal out of PCM. This happens only with ignition on. Truck is a 94. Any suggestions. Hate to buy a new PCM without trying other options to fix. Also just bought new batteries about a month ago. Die Hard Gold, 900 amp each.

BRAD

 

[Evan A. Beck]

Chances are, you'll need a new PCM. $450 from the dealer... You may want to try having them reprogram it first, and if that doesn't work, replace the PCM. If it were mine, I'd go ahead and replace the PCM, and be done with it.

 

[illflem]

Not sure exactly how things work without looking at a schematic, but could your intake manifold temp sensor or wiring be faulty, sending a false reading to the PCM?

 

[B KIRK]

Thanks guys for the replys.



Evan, if I have to "Bite The Bullet" and buy a new PCM, Mopar makes a reman for my year truck for $180. 00 . Was curious if anybody has one in thier truck, and if they are any good? Hate to buy something that could fail again, although a new one could fail also I guess.



illflem, thougth about air temp sensor, but after looking at schematic, and doing a search here, I kinda ruled that out. I still could be wrong about it, but there is 1 wire coming out of air temp sensor going to PCM to give a input signal. There are 2 wires coming out of PCM giving a ground signal to each relay to energize them. Number 2 relay works fine. It's just #1 that is getting a constant ground signal.



Anybody else have this type of problem? The TDR is a better place to try to solve most problems, rather than going to "some" dealers. Thanks

BRAD

 

[shendren]

DON'T BUY ANYTHING YET!!..... make sure that you tighten down the bolts on the solenoids that are mounted to the wheel well (on mine). had my tune up with jessup and sure enough, mine were loose as he predicted before he looked at them. said that most of the time this was the problem.....

 

[B KIRK]

Scott, thanks for the reply



The first thing I did, because of other posts on this problem, was to remove the relays to bench test them to make sure they weren't sticking. Both switched properly when energized. Reinstalled them and still had same problem. When testing wires, that is when I found PCM was sending signal to #1 relay. #2 works fine. Things point to the PCM as the problem, just wishing it was something else, (something less expensive).





Any other ideas?

HELP!!!!



Thanks. BRAD

 

[Double 6]

When you finally get the problem fixed, you might want to consider the Intake Heater System Saver from Practical Solutions.

They have some excellent products and great service.

 

[illflem]

Sadly the Intake Heater System Saver from Practical Solutions is only for 24 valves.