SPN 973 FMI 2 – Evobus retarder lever position not plausible Fault Code (Symptoms, Causes & Fix)
The SPN 973 FMI 2 fault code indicates a problem with the plausibility of the retarder lever position in Evobus systems. This diesel engine fault code suggests that the Engine Control Module (ECM) is receiving an implausible signal from the retarder lever position sensor, which could affect the retarder control system's operation.
What SPN 973 FMI 2 Means
The SPN 973 FMI 2 fault code specifically relates to the retarder lever position sensor. The ECM expects a certain range of signals from this sensor to determine the lever's position accurately. When the signal falls outside the expected range, the ECM flags this as a plausibility issue, indicating that the sensor's output does not match the physical position of the lever.
Common Causes of This Fault Code
- Failed retarder lever position sensor
- Wiring harness damage or shorts
- Corroded or loose connectors
- Faulty retarder control module
- Voltage reference faults
Symptoms Drivers May Notice
When the SPN 973 FMI 2 fault code is active, drivers may notice that the retarder does not engage or disengage as expected. There might be a lack of retarder response when the lever is moved, or the retarder may engage unexpectedly. Additionally, a warning light on the dashboard may illuminate, indicating a retarder system issue.
How Technicians Diagnose This Fault
Technicians begin diagnosing this fault by performing a visual inspection of the retarder lever position sensor and its associated wiring. They check for physical damage, wear, or signs of corrosion. Next, they perform a continuity test on the wiring harness from the sensor to the control module to identify any shorts or open circuits.
Using a multimeter, technicians verify the sensor's output voltage to ensure it is within the specified range. They also inspect connectors for corrosion or looseness, cleaning or replacing them as necessary. Finally, a diagnostic scan tool is used to check for additional related fault codes and to verify ECM data.
Common Misdiagnosis
A common misdiagnosis with the SPN 973 FMI 2 fault code is replacing the retarder control module without first verifying the integrity of the sensor and wiring. Technicians may also mistakenly assume a mechanical failure of the retarder without thoroughly checking the electrical components. Intermittent wiring issues due to vibration or movement can also be overlooked.
Can You Keep Driving?
While it may be possible to continue driving with the SPN 973 FMI 2 fault code active, it is not advisable. The retarder system may not function correctly, which can affect vehicle control during deceleration. In some cases, the fault may lead to engine derate or protection mode, impacting vehicle performance.
Mechanic's Diagnostic Tip
When diagnosing the SPN 973 FMI 2 fault code, always verify the sensor's power supply and ground circuits before replacing any components. This ensures that the sensor is receiving the correct voltage and can help avoid unnecessary part replacements.
Frequently Asked Questions
Q: What should I check first when diagnosing SPN 973 FMI 2?
A: Start with a visual inspection of the retarder lever position sensor and its wiring for any obvious damage or corrosion.
Q: Can a faulty retarder control module cause SPN 973 FMI 2?
A: Yes, a faulty retarder control module can cause this fault, but it is essential to verify sensor and wiring integrity first.
Q: Is it safe to drive with the SPN 973 FMI 2 fault code?
A: It is not recommended to drive with this fault code active, as it can affect the retarder system's operation and vehicle control.
