TedK Posted August 25, 2019 Report Share Posted August 25, 2019 My 1996 DeVille is effectively dead due to the failure of circuit 1807 (serial data). However, the failure is intermittent - it may disappear for an hour or so (meaning that the car starts fine), then will reappear (causing a no-start condition) - all without me touching anything. For this reason, this seems to be a failure of one of the modules on the serial data line. This doesn't seem to be a short to ground condition, as it doesn't ohm out to 0 resistance. Rather, my dvm shows variable resistance / variable voltage. I don't have a lab scope (hanging head in shame). When the circuit is bad, my OBD II scanner won't work - it can't read the serial data (power & ground are present on the DLC - the tool just can't make sense of the garbage). However, I can pull the codes from the message console. Then, out of the blue, the problem disappears and the car starts fine, with no current trouble codes! However, after a few minutes, the problem returns and the car again won't start. Here are the codes, pulled from the message console, when the car won't start: NO PCM DATA IP2750 C (PassKey II Data Comm Failure) AC2255 H AC2016 C No SDM Codes TC0072 C (IPC Serial Data Line Malfunction) TC0073 C (PCM / TCM - TCS Interface Malfunction) TC0077 C (PCM Serial Data Line Malfunction) No RSS Codes PZ2255 C (General Loss of Serial Data) IR2129 C No RFA Codes I tried a different PCM, but the problem didn't resolve (so I put the original PCM back in). My service manual says that circuit 1807 (serial data line) uses a Splice Pack (SP205, I think). However, I cannot find this splice pack. It's supposedly under the driver's side dash board, but I cannot find it! I've removed the parking brake mechanism, pulled back the carpeting, removed lower dash components, and searched everywhere up under the dash, but can't find the splice pack. This is an early-production 1996, so perhaps GM didn't actually use a splice pack until later-year productions? The purple wire (1807) from the DLC enters a small wire harness, then seems to merge into a larger wire harness, and I lose track of it from there (but it "seems" to pass through the firewall - not sure if that purple wire is really 1807). Please - I'm open to suggestions! My next effort is to remove the rear seat back (again), and start unplugging controller modules one at a time, hoping for the problem to disappear with a module (I did this a year ago, without success; yes, the car has been down for a year). Quote Link to comment Share on other sites More sharing options...
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