The Cummins ISM code 399 manual is a 5-page diagnostic PDF for the actuator circuit on the ISM CM570 (1999–2002) engine. It covers the rear timing actuator that the electronic control module (ECM) pulses to control fuel timing on the fuel delivery housing.
Cummins ISM code 399 document details
| Brand | Cummins |
| Model coverage | ISM CM570 (1999–2002) |
| System / group | Actuator circuit — DTCs |
| DTC number | 399 |
| PID / SPN | S084 / 1245 |
| FMI | 6/6 |
| Warning lamp | YELLOW |
| Pages | 5 |
| File format | |
| Language | English |
Document table of contents
- Circuit description and component location
- Shop talk on failure modes
- Actuator harness pin inspection
- Actuator resistance measurement
Applicable truck models
This procedure applies to the ISM CM570 (1999–2002) engine and the shared CM570 fuel-system platform found in on-highway trucks. The same fault-code logic is carried across related CM570 engine families of that era. For engine identification and factory service references, see the manufacturer at the Cummins official website.
Who needs this Cummins ISM code 399 manual
The document explains that each timing actuator connects to the ECM by a supply and a return wire and that the normally closed solenoid valve opens only on an electrical pulse during metering. It places the rear timing actuator as the third actuator from the front of the engine. For this fault the listed failure modes are a short circuit to battery, low actuator resistance, or a short between the supply and return wires. The steps inspect the actuator harness connector pins and then measure actuator resistance.
This guide suits diesel technicians and workshop owners who face a rear timing actuator short or low-resistance fault and want the exact pin and resistance checks. It reads as fault code 399 troubleshooting steps for the actuator circuit, so the ECM circuit diagnosis stays ordered and evidence-based rather than a parts-swap guess, and it maps cleanly onto a scan-tool session on the CM570 engine platform.
The full PDF is available in the DiagTechPro manuals library, where a free account is required to download it.
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