CaddyPhil Posted August 28, 2015 Report Share Posted August 28, 2015 My 1996 Deville has the engine light on and will not pass emissions. My dad's car, he thinks its a bad ground? The repair shop wants to replace the PCM at a cost of $502 pluss around $300 for installation and programming. I found one on Ebay for $89.95 programmed. Anyone familiar with this issue? Please help.. Phil Link to comment Share on other sites More sharing options...
Logan Posted August 28, 2015 Report Share Posted August 28, 2015 P1634. Ignition 1 switch circuit. The PCM is powered with 5 power feeds. Two of these feeds are from the battery, the other three are from the ignition switch and are called Ignition 1, Ignition Supplement and Ignition 0. Ignition 1 and Ignition Supplement are powered any time the key is in the CRANK , RUN or ACC positions. Ignition 0 is powered in ALL key positions except LOCK and CRANK. This diagnostic test is used to monitor the voltages received by the PCM at connector C1 terminals 18 and 19. When the engine is running, the PCM will compare the Ignition 1 voltage it receives at connector C1 terminal 19 to the Ignition 0 voltage it receives at connector C1 terminal 18. If the Ignition 1 and Ignition 0 voltages are more than 2 volts different for 5 seconds, DTC P1634 will set. I would try a new ignition switch before doing anything. Logan Diagnostic LLC www.airbagcrash.com www.logandieselusa.com www.ledfix.com www.ledfix.com/yukontaillightrepair.html www.ledfix.com/ledreplacements.html www.ledfix.com/j42385toolrental.html Link to comment Share on other sites More sharing options...
rockfangd Posted August 28, 2015 Report Share Posted August 28, 2015 See if someone added a remote car starter and hacked into the wires to the ignition. You can also verify outputs to the ignition circuits from the ignition GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
winterset Posted August 29, 2015 Report Share Posted August 29, 2015 Yes, i second the ignition switch as the culprit. We have seen these problems popping up on the mid 90's cars recently. 20 years and thousands of cycles on a switch is pretty good if you ask me. Link to comment Share on other sites More sharing options...
rockfangd Posted August 30, 2015 Report Share Posted August 30, 2015 lol. I agree. I have not had one go bad yet. My truck is 25 years old and works fine. Saginaw column. The Saginaw columns were very reliable other than the occasional loose bolts on the tilt column, a more common problem on the trucks. The other common problem is the passlock wires breaking in the column after so much flexing GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
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