SPN 972 FMI 2 – Throttle inhibit switch signal not plausible due to excess vehicle speed Fault Code (Symptoms, Causes & Fix)
The SPN 972 FMI 2 fault code indicates a problem with the throttle inhibit switch signal, specifically that it is not plausible due to excess vehicle speed. This diesel engine fault code suggests that the Engine Control Module (ECM) is receiving a signal from the throttle inhibit switch that doesn't align with the current vehicle speed, potentially leading to operational issues.
What SPN 972 FMI 2 Means
When the SPN 972 FMI 2 fault code is active, it points to an inconsistency between the throttle inhibit switch signal and the vehicle's speed. The ECM expects the throttle inhibit switch to provide a signal that matches the vehicle's operational parameters. If the signal is not plausible, it can indicate a fault in the electrical circuit or the switch itself, leading to potential throttle control issues.
Common Causes of This Fault Code
- Faulty throttle inhibit switch
- Wiring harness issues such as chafing or corrosion
- Poor electrical connections at the throttle inhibit switch
- Faulty ECM input
- Voltage reference faults
Symptoms Drivers May Notice
Drivers may experience symptoms such as unexpected throttle response, reduced engine performance, or the vehicle entering a limp mode. These symptoms occur because the ECM cannot accurately control the throttle due to the implausible signal.
How Technicians Diagnose This Fault
Technicians begin by performing a visual inspection of the throttle inhibit switch for any physical damage or wear. Next, they check the wiring harness for signs of chafing, corrosion, or loose connectors. Using a multimeter, they verify the voltage and ground signals at the throttle inhibit switch. A continuity test is performed on the wiring harness from the switch to the ECM to ensure there are no breaks or shorts. Finally, technicians use diagnostic software to verify ECM data and ensure proper signal reception.
Common Misdiagnosis
A common misdiagnosis is replacing the throttle inhibit switch without verifying the integrity of the wiring. Technicians may also mistakenly assume a mechanical issue with the throttle pedal or linkage, overlooking potential electrical faults.
Can You Keep Driving?
While the vehicle may continue to operate, driving with the SPN 972 FMI 2 fault code active is not recommended. The fault can lead to reduced engine performance or cause the vehicle to enter a protection mode, potentially resulting in unsafe driving conditions.
Mechanic's Diagnostic Tip
Always verify the wiring integrity before replacing the throttle inhibit switch. Intermittent wiring issues due to vibration are common and can lead to misdiagnosis if not thoroughly checked.
Frequently Asked Questions
Q1: What tools are needed to diagnose SPN 972 FMI 2?
A: A multimeter and diagnostic software are essential for testing voltage, continuity, and ECM data.
Q2: Can a faulty ECM cause SPN 972 FMI 2?
A: Yes, a faulty ECM input can cause this fault code, but it should be considered after verifying all other potential causes.
Q3: Is it safe to ignore the SPN 972 FMI 2 fault code?
A: Ignoring this fault code is not advisable as it can lead to reduced engine performance and unsafe driving conditions.
