SPN 602 FMI 19 – J1939 Cruise Control Accelerate Switch Signal from Source #1, #2, or #3 is erratic Fault Code (Symptoms, Causes & Fix)
The SPN 602 FMI 19 fault code indicates an erratic signal from the J1939 cruise control accelerate switch, sourced from #1, #2, or #3. This diesel engine fault code suggests that the Electronic Control Module (ECM) is receiving inconsistent or unexpected signals from the cruise control system, potentially affecting its operation.
What SPN 602 FMI 19 Means
This fault code is triggered when the ECM detects an irregular signal from the cruise control accelerate switch. The switch is responsible for sending a signal to the ECM to increase vehicle speed when cruise control is engaged. An erratic signal can disrupt the cruise control function, leading to inconsistent vehicle speed control.
Common Causes of This Fault Code
- Faulty cruise control accelerate switch
- Intermittent wiring or connector issues in the cruise control circuit
- Corrosion or damage at the connector terminals
- Faulty ECM/BCM receiving the signal
- Voltage reference faults
Symptoms Drivers May Notice
Drivers may experience inconsistent cruise control operation, such as unexpected acceleration or deceleration. The cruise control may disengage unexpectedly, or the system may fail to maintain the set speed.
How Technicians Diagnose This Fault
Technicians begin by performing a visual inspection of the cruise control accelerate switch and its associated wiring for any visible damage or corrosion. Using a multimeter, they check for continuity and proper voltage at the switch connector. The wiring harness from the switch to the ECM/BCM is inspected for wear, damage, or loose connections. A diagnostic tool is used to monitor the J1939 data bus for erratic signals or communication errors related to the cruise control system. Finally, they check for any additional fault codes that may indicate a broader issue with the vehicle's electrical system.
Common Misdiagnosis
One common mistake is replacing the cruise control accelerate switch without verifying the integrity of the wiring and connectors. Another is assuming the issue lies with the ECM/BCM without first ruling out simpler electrical faults. Technicians may also overlook intermittent wiring issues that only occur under certain conditions, such as vibration or temperature changes.
Can You Keep Driving?
While the truck may still be operable, driving with this fault code active can lead to unpredictable cruise control behavior, which may affect driving safety. It is advisable to address the issue promptly to ensure reliable cruise control operation.
Mechanic's Diagnostic Tip
Always verify the integrity of the wiring and connectors before replacing the cruise control accelerate switch. Intermittent issues are often caused by loose or corroded connections, which can be resolved without part replacement.
Frequently Asked Questions
Q: What tools are needed to diagnose SPN 602 FMI 19?
A: A multimeter and a diagnostic tool capable of reading J1939 data are essential for diagnosing this fault code.
Q: Can a faulty ECM cause SPN 602 FMI 19?
A: Yes, a faulty ECM can cause this fault code, but it is important to rule out simpler electrical issues first.
Q: Is it safe to drive with an erratic cruise control signal?
A: While the vehicle may still be drivable, it is recommended to fix the issue to ensure safe and reliable cruise control operation.
