Cummins ISM code 3733 is the Cummins ISM CM871 diagnostic entry for fault code 3733, crankcase breather filter heater circuit (SPN 862, FMI 3). This page summarises what the code reports, the circuit involved, and the official Cummins troubleshooting document behind it, taken from the fault-code publication for Cummins ISM CM871 engines. It is written for mechanics and workshop owners who want to confirm the code before ordering parts.
What Cummins ISM code 3733 means
Fault code 3733 is logged against crankcase breather filter heater circuit. The document reports a warning lamp, which tells the driver to have the engine serviced soon. The electronic control module (ECM) controls the crankcase breather filter heater by sending a signal. The ECM will only command the crankcase breather filter heater ON under certain operating conditions.
Circuit description and component location
Component location. The crankcase breather filter heater is located on the front cover of the crankcase breather filter housing.
The official diagnostic identifiers for this fault let you match the code across scan tools and repair records:
- SPN: 862
- FMI: 3
- Lamp: AMBER
The document walks the technician through the numbered troubleshooting steps for this circuit, from connector inspection to resistance and short-to-ground measurements, so the fault can be confirmed before any part is replaced. Each step ends in a yes or no branch that either clears the code or sends you to the next check, which keeps the diagnosis systematic and avoids guesswork on the bench.
How to diagnose Cummins ISM code 3733
Start by reading the live codes with an approved Cummins diagnostic tool and confirming the code is active. Inspect the harness connector pins for bent or corroded terminals, pushed-back pins and moisture, then follow the manufacturer resistance and continuity checks in the order given. Diagnostic procedures for Cummins ISM CM871 engines are published by Cummins; see the Cummins official website for engine documentation and authorised service-network support.
Official references and part numbers
Refer to the Cummins fault-code troubleshooting publication for the exact repair procedure. Use these identifiers to order the correct Cummins service publication and tooling, and to log the repair accurately for the fleet record. The full PDF is filed in the DiagTechPro manuals library for mechanics and workshop owners to download.
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