Cummins fault code 3734
Crankcase Breather Filter Heater Circuit: circuit voltage low / shorted low
What it means
Cummins' description: Crankcase Breather Filter Heater Circuit - Voltage below normal, or shorted to low source.
SPN 862 is Crankcase breather Heater Circuit. FMI 4 means the voltage on the circuit is lower than possible for a good sensor, usually a short to ground, a damaged harness, or a failed sensor.
The crankcase ventilation system relieves pressure from blow-by gases. The ECM monitors crankcase pressure, and some systems have a heated breather to keep it from freezing.
What the lamp means
An amber (yellow) warning lamp means the engine can usually keep running, but the fault should be repaired soon, ideally the same day.
Green, yellow, red: three ways this can look
The same code can be a quick fix or a reason to shut down. Match your situation to the closest example.
Keep an eye on it
A one-time crankcase code in freezing weather that cleared once warm.
Schedule a repair
The code keeps returning or oil is seeping from seals. Service the breather soon.
Stop and get help
Oil blowing out of the dipstick tube, heavy blow-by smoke, or a stop lamp. Shut it down. High crankcase pressure can mean serious internal wear.
Common causes
FMI 4 is an electrical or signal fault, so start with the circuit:
- Crankcase pressure sensor failed or wiring fault
- Breather heater circuit fault
If the circuit checks out, the reading may be real. Other possibilities: plugged crankcase breather or filter; frozen breather in cold weather; disconnected ventilation hose.
What you can check before calling
- Check that the breather hose is connected and not kinked or frozen
- Look for oil being pushed out of the dipstick tube or seals
- Note heavy smoke from the breather tube
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers.
Engines and sources
Listed by Cummins for: QSX 15, QSG 12. Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.
Same SPN, other failure types
Related Crankcase and ventilation codes
- 3377 SPN 5396 FMI 31
Engine Crankcase Ventilation Hose Disconnected: condition exists - 4286 SPN 520595 FMI 3
Closed Crankcase Ventilation System Pressure Sensor: circuit voltage high / shorted high - 4287 SPN 520595 FMI 4
Closed Crankcase Ventilation System Pressure Sensor: circuit voltage low / shorted low - 4288 SPN 520595 FMI 2
Closed Crankcase Ventilation System Pressure: erratic or intermittent signal - 2699 SPN 520320 FMI 7
Crankcase Depression Valve: not responding / out of adjustment - 1974 SPN 101 FMI 15
Crankcase Pressure: reading above normal (least severe)
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does Cummins fault code 3734 mean?
Cummins fault code 3734 is J1939 SPN 862 FMI 4: Crankcase Breather Filter Heater Circuit - Voltage below normal, or shorted to low source. In plain terms: crankcase breather filter heater circuit: circuit voltage low / shorted low.
Can I keep driving with Cummins code 3734?
Usually for a short time, if the engine runs normally and no other warnings are on. Get it diagnosed soon, because many amber codes lead to a derate if ignored. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 3734?
SPN 862 identifies the part or system (Crankcase breather Heater Circuit). FMI 4 describes the type of failure: circuit voltage low / shorted low.
What usually causes Cummins code 3734?
The most common causes are: crankcase pressure sensor failed or wiring fault; breather heater circuit fault.
Diesel down in the Midlands?
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