This Cummins fault code 768 document is a troubleshooting guide for the output device driver circuit used to control the transmission shift modulation signal. It identifies PID S009, SPN 923, FMI 11, and explains checks for the transmission shift modulator, OEM harness, ECM connector, and related wiring faults. The file is a short diagnostic procedure intended for service use with an appropriate diagnostic tool.
Official Cummins fault code 768 document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; output device driver circuit; transmission shift modulation |
| Publication no. | Not shown in the extract |
| Year/Revision | Unknown; document copywrite 2017 |
| Pages | 3 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 768
- PID: S009
- SPN: 923
- FMI: 11
- OUTPUT DEVICE DRIVER (TRANSMISSION SHIFT MODULATION)
- Output Device Driver Circuit
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A: transmission shift modulator inspection and OEM test
- Step 2A: OEM harness and connector inspection
- Step 2B: open circuit resistance check from pin 21
- Step 2C: short circuit to ground check
- Step 2D: pin-to-pin short circuit check
- Step 3A: disable fault code and verify inactive status
- Step 3B: clear inactive fault codes
Applicable truck models
This procedure applies to Cummins ISB CM550 (1990-94) diagnostic coverage where Fault Code 768 is reported for the output device driver used by the ECM to control the transmission shift modulation signal. The extract does not name a specific truck make, chassis model, or transmission model; it directs the technician to an OEM diagram for the location of the transmission shift modulator and to OEM instructions when powering the modulator directly from the battery. For official engine information, see Cummins official website.
Who needs this Cummins fault code 768 manual
Mechanics, fleet technicians, and workshop owners need this file when diagnosing a failed engine harness, a bad ground at the transmission shift modulator connector, or a bad transmission shift modulator. It is also useful when confirming resistance limits such as less than 10 ohms for the open circuit check and more than 100k ohms for ground or pin-to-pin short checks.
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