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oddgca
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Jul 12, 2012, 8:47 PM
Post #1 of 12
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I want to exchange the PCM (computer) in the Mercury Sable 97 3.0 l. The newer module has the same numbers as the the one installed. It has also the same large number sticker "KQQ1". Can it be installed without problems?
The reason for the exchange is that the cruise control does not work anymore. I checked the wiring. It is in order. The signal from the speed sensor however is a sine wave. It seems to be not recogniced from the speed control module. On a Taurus 2000, which has the same engine as the one in the Sable 97, the signal is a square wave. The PCM seems to supply an underlaying wave former and changes the sine wave coming from the vehicle speed sensor into a square wave.
Any help in this matter is greatly appreciated.
Otto
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 13, 2012, 3:23 AM
Post #2 of 12
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Re: PCM for Sable97
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It will have to be programmed by the dealer before it will run.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Jul 13, 2012, 5:08 AM
Post #3 of 12
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Re: PCM for Sable97
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I don't understand why you want to replace the PCM for a cruise control problem. The PCM has nothing to do with the cruise control. The cruise control system has it's own control module that recieves vehicle speed information from the vehicle speed sensor and gets inputs from the steering wheel controls and brake switch. PCM has nothing to do with this. Where are you making your checks?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 13, 2012, 5:09 AM)
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oddgca
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Jul 16, 2012, 8:42 AM
Post #4 of 12
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Re: PCM for Sable97
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With the plug of the speed module unplugged at the Sable, I don't receive any signal on pin 3 of the plug with the key in start and run.
Comparing it with the Taurus2000 (my wife's car), which has the same engine, I measured 11.43V at start and 13.37 V in run.
After checking all the wiring I made a running test.
Lifting up the front part of the cars, removing the tires and measuring terminal 3 during at low speed running (about 22 km/h). On the Sable I measured with the oscilloscope a sine wave in running.
On the Taurus I measured in start position, a small square wave with high frequency. In running it was a large square wave with about the same amplitude and wave lengths as the sine wave of the Sable.
I assume therefore, that the PCM is supplying an underlaying square wave former from its terminal 58 on the Taurus2000.
Interesting is, that on the Sable the odometer reads the correct vehicle speed during riding. The odometer in the dash port seems to read the sine wave coming from the vehicle speed sensor.
It might be interesting to know, what signal the vehicle speed sensor supplies. Is it a sine wave or a square wave?
Therefore I assume, that the the PCM is defective. Unfortunatley I don't have a schematic of the PC board of the PCM to dig a bit deeper into the function of the PCM.
oddgca
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Hammer Time
Ultimate Carjunky
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Jul 16, 2012, 9:04 AM
Post #5 of 12
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Re: PCM for Sable97
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The PCM isn't even in the circuit. Pin #3 goes to the VSS.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Jul 16, 2012, 9:04 AM)
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Discretesignals
Ultimate Carjunky
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Jul 16, 2012, 9:07 AM
Post #6 of 12
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Re: PCM for Sable97
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The vehicle speed sensor on the 97 is a VR sensor that produces an ac voltage signal. If your speedometer is working and you don't have any speed sensor codes stored in the PCM, then your vehicle speed signal is reaching those things. If it is reaching the speed control module, then you have another problem. Like I stated earlier the PCM has nothing to do with the operation of the cruise control. The only thing they have in common is that they both get the vehicle speed signal from the same sensor.
You really need a wiring diagram. Comparing two different years is going to get you in trouble.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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oddgca
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Jul 16, 2012, 12:52 PM
Post #7 of 12
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Re: PCM for Sable97
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I thank you very much for your fast reply.
I have to look a bid closer into the matter. Presently I don't have access to the workshop manual Sable 1997. I have only the Haynes Repair Manual for Taurus and Sable 1996 thru 2001.
The wiring diagrams in there are the in general the same for both models (Pages 12-23,24,25,26 and 45). On pages 6-15 and 16 is also written about the vehicle speed sensor(VSS). The VSS and the OSS (output Shaft Speed sensor, for models 2000 and later) produces a sine wave ac signal, as I noticed on the Sable 97. Why do I measure a ac square wave signal on the Taurus 2000? Can be the Generic Electronic Module the cause for it?
You will hear from me again in a few days.
Otto
oddgca
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oddgca
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Jul 17, 2012, 2:25 PM
Post #9 of 12
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Re: PCM for Sable97
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Thank you again for the information.
I might be on the wrong path about the problem, since I assumed, that the electrical wiring and circuits of the Sable 97 and the Taurus 2000 are the same. I will try to get the diagrams for the Taurus 2000.
Now it seems, that the speed control module is the problem. I checked all the connections and switches around the module. Everything looks fine. I can even switch the cruise control on and receive on the dash board the indication that the cruise control is engaged.
The problem started month ago. First intermittent. It switched off by itself and I had to switch it on again. Now it does not work at all. What can be the cause?
Otto
oddgca
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oddgca
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Jul 17, 2012, 4:59 PM
Post #10 of 12
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Re: PCM for Sable97
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I have to thank you again very much.
As I told you on the previous reply, I was on the wrong track by comparing the function of the speed control modules of the Sable3 97 with the Taurus 2000.
The problem is the wire from the Speed Control Deactivate Switch to plug terminal 9 of the Speed Control Module. This wire is interconnected at In-line plug C222 pins 636. The connection must be bad, because not the full voltage reaches the Speed Control Module. I could not find the In-line connector C222. It must be well hidden behind the dash board. By installing a temporary jumper the speed control works. Tomorrow I will drill a hole into the firewall and feed the wire thru for a more final solution.
Otto
oddgca
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Discretesignals
Ultimate Carjunky
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Jul 17, 2012, 5:21 PM
Post #11 of 12
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Re: PCM for Sable97
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Your welcome. You must have gotten some better schematics. Before you go drilling through the firewall or looking for connector C222, you might want to go to the speed control deactivation switch and check to make sure it isn't open or incorrectly adjusted. Check to make sure you have power before and after the switch with brake pedal fully disengaged.
636 is the circuit number. The pin out is in the connector view for C222.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 17, 2012, 5:44 PM)
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oddgca
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Jul 18, 2012, 7:22 AM
Post #12 of 12
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Re: PCM for Sable97
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I have good schematics for the Sable 97, but not for the Taurus 2000. This started all the confusion.
The speed control deactivation switch works fine. By unplugging it and putting a jumper into the female side of of the plug, still not the full voltage appeared on pin 9 of the speed control module.
You are right, the pin effected on C222 is not 636. It is pin 13.
Otto
oddgca
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