This document is a Cummins exhaust brake fault troubleshooting sheet for Fault Code 243 on Cummins ISB CM550 engines. It covers the exhaust brake relay supply circuit, connector inspections, resistance checks, harness fault isolation, and final diagnostic-tool verification.
Official Cummins exhaust brake fault document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; Exhaust Brake Supply Circuit; Exhaust Brake Relay Supply Circuit |
| Publication no. | Not shown in extract |
| Year/Revision | Unknown |
| Pages | 5 |
| File size | 0.4 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 243
- PID: P121
- SPN: 513
- FMI: 4
- EXHAUST BRAKE SUPPLY CIRCUIT
- Exhaust Brake Relay Supply Circuit
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A: Inspect the engine harness and the ECM connectors
- Step 1B: Check for an open circuit from pin 42 of the ECM connector to pin O of the 23-pin OEM harness connector
- Step 1C: Check for a short circuit to ground from pin 42 in the engine harness to engine block ground
- Step 1D: Check for a short circuit between pins from pin 42 to all other pins in the ECM connector
- Step 2A: Inspect the OEM harness, 23-pin connector, and the exhaust brake connector
- Step 2B: Check for an open circuit from pin O of the 23-pin OEM connector to pin 1 of the exhaust brake connector
- Step 2C: Check for a short circuit to ground from pin O of the 23-pin connector to the engine block ground
- Step 2D: Check for a short circuit from pin to pin
- Step 3A: Disable the fault code and verify Fault Code 243 is inactive
- Step 3B: Clear the inactive fault codes using the diagnostic tool
Applicable truck models
This PDF applies to Cummins ISB CM550 engines in the DTC group identified in the file information, with year coverage shown as 1990-94. The extract does not list truck makes or chassis models, and it directs the technician to the original equipment manufacturer diagram for the location of the engine brake. For manufacturer information, visit the Cummins official website.
Who needs this Cummins exhaust brake fault manual
Mechanics, electrical diagnosticians, and workshop owners need this Cummins exhaust brake fault manual when Fault Code 243, PID P121, SPN 513, FMI 4 is present and the exhaust brake relay supply circuit must be tested. The procedure is centered on ECM pin 42, OEM 23-pin connector pin O, exhaust brake connector pin 1, resistance limits, connector condition, and final confirmation with a diagnostic tool.
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