Seems like the pcm conrtol relay is bad

Tiny
DAVID GABRIEL
  • MEMBER
  • 1998 FORD WINDSTAR
  • 160,000 MILES
Seems like the pcm conrtol relay is bad.(The one under the air intake part of the cruise control) Check engine light comes on after the battery is off for a while, even started for about 1 min then died, no mil now. Checked cam shaft positioning sensor. 10-12 pulsing when cranking 10 or os at rest. Key on. The relay in the enging compartment labeled PCM relay, gets power on its coil at random. Interior fuse 20 good. The problem seems to be between the interior fuse and the PCM relay in the engine power dist box. How do I test that module. It is not mentioned in the Haynes book I am not ruling out possibility of ignition switch. Please help.
Monday, December 24th, 2012 AT 6:18 PM

7 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Make srue to check fuse r in underhood fuse box along with pcm relay they may be bad and that is power source for truck. Also scan for codes if mil comes oand try freeze frame it may pick it up. Check resistance of crank sensor, it shodl be betwen 300 & 800 ohms. If higher or lower it could e your problem as well as the connection.
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Monday, December 24th, 2012 AT 6:56 PM
Tiny
DAVID GABRIEL
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All fuses checked out early in all this. No codes stored. No freeze frame data. Relay is good swapped it out with another just for fun. I'll check crank sensor, but what about the question I asked? Is there a way to check the PCM relay module? The one that is mounted on the cruise control cable/gear assy. It's under the air intakenear the power distribution box. Also.I've removed the bottom of the underhood fuse box looking for loose connections. Nothing.
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Monday, December 24th, 2012 AT 7:12 PM
Tiny
DAVID GABRIEL
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Also, I cleaned the ground strap and ground wire at the shock tower by the PCM( not the ones at the battery. They are all clean ). It wasn't real dirty but was worth cleaning.A few times over the past few months, the temp guage was not reading. As if the sensor had lost a wire, but on next start/up and 99% of the time works correctly.
Dave
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Monday, December 24th, 2012 AT 8:55 PM
Tiny
HMAC300
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It's for cruise control only as it only has vss input and output in it then ties intor cruise Most pcms are trial and error or if you have a pro type scan tool it can check everything but the pcm. And it leaves it to just an experieince or tryit and see what happens. Still think y ou ought to go to crank sensor or connetion problem even on cam sensor. Also have your tried to reset your anti theft as that can do it as well.
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Monday, December 24th, 2012 AT 9:00 PM
Tiny
DAVID GABRIEL
  • MEMBER
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Thanks, As I mentioned (first question) the cam sensor pulses when cranking 10-12v connection seems good. No anti theft on vehicle, raining now here in Fayetteville. Crank sensor will have to wait. So long as the module mounted on the cruise control does not effect starting in any way, I have to take that as my answer as to wheather or not it can be tested. So from your last, can I assume that the only things that will keep the PCM from getting power ie(THE FEED FROM THE INTERIOR FUSE BOX # 20 TO THE RELAY COIL IN THE POWER DISTRIBUTION BOX and keep the "service engine soon" light out. Would be the Cam shaft or crank shaft sensor?RE. First question. Stated relay in that box does not always energize, and when it does not, no check engine light/no power to the PCM, you're not answering my direct questions.
Dave
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Monday, December 24th, 2012 AT 9:37 PM
Tiny
ASEMASTER6371
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One way to verify if the pcm is functioning is to monitor the 5 volt reference signal when the key is on when the issue is happening. You can use the tps sensor as it is easy to get to.

As far as the relay, it grounds with the key on to send power to the items in the diagram.

There is a diode in the pcm in line with the 12 volt signal as you see. Once it is grounded, it controls a lot of power sources to different items.

Look at the diagram I sent you.

Roy
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Monday, December 24th, 2012 AT 9:48 PM
Tiny
HMAC300
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In my very first reply I said to check fuse r in underhood fuse box as that sendspower to pcm relay not fuse 20 inside car. Iguess I shold have sent a pic fuse 20 also supplies it and that is the one tha goes through the diode that roy has pointed out. If the diode is bad you'l get no power. Evidently I shold have sent the diagram to begin with. Besides teh pcm it powers a few other things like shift solenoids, etc. Fuse 20 sends power to teh ignitin coils as well.
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Monday, December 24th, 2012 AT 11:16 PM

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