Cadillac Repair: BCM to ECM, no communication, digital voltmeter, memcal

Question
I have a 1990 Caddillac Sedan Deville 4.5 ltr. I have found eng. code F32. If there is no communication between the BCM and ECM, will this stop the vehicle from starting?

I have spark and fuel delivery. Keep in mind that eng. codes E12, E52 and E65, were previously stored in memory but I erased those and I now only get the F32 code.

Thanks
Jonathan

Answer
Hi Jonathan, I haven't heard of that code causeing a no start condition. However diagnoseing that code can be alittle bit tricky. If there was a FF32 that means the problem is happening now whereas F32 means it happened some time ago. Knowing what the service engine light does when cranking and if the instantanious fuel economy is varrying or at 0 mpg when driveing is also a clue.

   So basically what it comes down to is shorted wires between the ECM and BCM, a bad ECM or BCM or a faulty prom or memcal inside the ECM or BCM. Installing a digital voltmeter into the data line and looking for a varrying voltage is what needs to be done to determine who doesn't want to talk.

    The other codes might cause a problem with a no start. For example the EE12 showed up it could mean that the distributor module, pick-up coil, distributor wireing harness inside the distributor cap or the ECM could be bad and cause a no start.

   The E52 means the ECM lost battery voltage. Wether the battery was disconnected, the ECM was unplugged or was defective internally would set that code and again a nostart.

    The E65 is a cruise control servo sensor position sensor code. However replaceing the ECM because of it isn't in their trouble tree.

     What I might recommend is to lower the ECM down from under the dash behind the glovebox and with the engine running tap or rap on the case with your knuckles and see if the service engine light comes on or flickers. If it does there is a problem with the circuitboard and replaceing the ECM might keep those codes from comming back. The engine could also quit running. One word of caution is that useing a hammer or other tool to tap on the case could damage an otherwise good ECM so don't tap any harder than you would on someones shoulder to get their attention is the best way to describe what needs to be done.  The ECM can be accessed by removeing the black plastic under dash panel and is seen behind the glovebox. 2 10mm nuts and it should come down. If not unplug it with the key off and when it is down on the floor plug it back in and then start the engine and then start tapping all over the case. If you do need to replace it just remember to transfer over the prm to the replacement ECM or the engine won't start.

    Hope that helps and let me know if you need anymore help. Bill