SPN 1073 FMI 4 – Jake Brake Stage 2 Circuit Failed Low Fault Code (Symptoms, Causes & Fix)
The SPN 1073 FMI 4 fault code indicates a problem with the Jake Brake Stage 2 circuit, specifically that the circuit has failed low. This diesel engine fault code suggests that the Engine Control Module (ECM) is detecting a lower than expected voltage in the Jake Brake Stage 2 circuit, which can affect the engine's braking performance.
What SPN 1073 FMI 4 Means
The SPN 1073 FMI 4 diagnostic trouble code is related to the engine brake system, specifically the Jake Brake Stage 2 circuit. The ECM monitors the voltage levels in this circuit to ensure proper operation. A 'failed low' condition means the ECM is seeing a voltage lower than the acceptable range, which could indicate an electrical issue such as a short or open circuit.
Common Causes of This Fault Code
- Faulty Jake Brake solenoid
- Open or short in the Jake Brake Stage 2 circuit wiring
- Corroded or loose electrical connectors
- Faulty Engine Control Module (ECM)
Symptoms Drivers May Notice
When the SPN 1073 FMI 4 fault code is active, drivers may notice reduced engine braking performance, especially when the Jake Brake is engaged. The engine may not slow down as expected, leading to longer stopping distances.
How Technicians Diagnose This Fault
Technicians begin diagnosing this fault with a visual inspection of the Jake Brake solenoid and associated wiring for any signs of damage or corrosion. Next, they use a multimeter to check for continuity and resistance in the Jake Brake Stage 2 circuit. Inspecting and cleaning all connectors related to the Jake Brake system is crucial to ensure good electrical contact. Diagnostic software can be used to command the Jake Brake Stage 2 on and off, verifying solenoid operation. Finally, checking the ECM for additional fault codes helps identify if there are broader issues affecting the system.
Common Misdiagnosis
Technicians often make the mistake of replacing the Jake Brake solenoid without verifying the integrity of the wiring. Another common error is assuming a mechanical issue with the Jake Brake when the fault is electrical. Overlooking corroded connectors as a potential cause is also a frequent oversight.
Can You Keep Driving?
While the truck may still be operable with the SPN 1073 FMI 4 fault code active, it's not advisable to continue driving without addressing the issue. The reduced engine braking performance can lead to safety concerns, especially in situations requiring effective braking. Additionally, prolonged operation with this fault may lead to further electrical issues or engine derate.
Mechanic's Diagnostic Tip
Always verify the integrity of the wiring and connectors before replacing any components. A simple cleaning of corroded connectors or repairing a damaged wire can often resolve the issue without the need for part replacement.
Frequently Asked Questions
- What does SPN 1073 FMI 4 indicate? It indicates a low voltage condition in the Jake Brake Stage 2 circuit.
- Can a faulty ECM cause this fault code? Yes, a faulty ECM can misinterpret signals and trigger this fault code.
- Is it safe to drive with this fault code active? It's not recommended due to potential safety risks from reduced engine braking performance.
