Sidebar

SPN 171 FMI 14 – J1587 Ambient Air Temp Sensor Data Not Received This Ign Cycle Fault Code (Symptoms, Causes & Fix)

The SPN 171 FMI 14 fault code indicates that the Engine Control Module (ECM) did not receive data from the ambient air temperature sensor during the ignition cycle. This diesel engine fault code suggests a communication issue between the sensor and the ECM, which could affect engine performance and diagnostics.

What SPN 171 FMI 14 Means

The SPN 171 FMI 14 diagnostic trouble code is triggered when the ECM fails to receive a signal from the ambient air temperature sensor. This sensor is responsible for providing the ECM with the current outside air temperature, which is crucial for various engine management functions. When the ECM does not receive this data, it may default to a pre-set value, potentially affecting engine efficiency and emissions.

Common Causes of This Fault Code

  • Failed sensor
  • Wiring harness damage
  • Connector corrosion
  • ECM signal problems
  • Voltage reference faults

Symptoms Drivers May Notice

When the SPN 171 FMI 14 fault code is active, drivers may not notice immediate performance issues. However, incorrect ambient temperature readings can lead to inefficient fuel combustion, increased emissions, and potential engine derate if the ECM relies heavily on this data for other calculations.

How Technicians Diagnose This Fault

Technicians begin diagnosing the SPN 171 FMI 14 fault by performing a visual inspection of the ambient air temperature sensor and its wiring. This includes checking for physical damage, corrosion, or loose connections. Next, they verify the sensor's power supply and ground circuits using a multimeter. If applicable, they check the 5-volt reference circuit.

Technicians then perform a continuity test on the wiring from the sensor to the ECM to ensure there are no breaks or shorts. Using diagnostic software, they verify ECM data and check for additional fault codes that might indicate broader communication issues. Only after confirming the integrity of the wiring and sensor do they consider replacing components.

Common Misdiagnosis

A common misdiagnosis with the SPN 171 FMI 14 fault code is replacing the ambient air temperature sensor without first checking the wiring harness and connectors. Another mistake is assuming a faulty ECM without verifying the sensor and wiring integrity. Technicians may also overlook software or calibration updates that could affect sensor communication.

Can You Keep Driving?

While the SPN 171 FMI 14 fault code may not immediately impact drivability, it is advisable to address the issue promptly. Prolonged operation with incorrect ambient temperature data can lead to inefficient engine performance and increased emissions. In some cases, it may trigger engine derate or protection modes if the ECM relies on this data for critical functions.

Mechanic's Diagnostic Tip

Always verify the integrity of the wiring harness and connectors before replacing the ambient air temperature sensor. Corrosion and loose connections are common culprits that can mimic sensor failure. Use dielectric grease on connectors to prevent future corrosion issues.

Frequently Asked Questions

Q: Can a faulty ambient air temperature sensor affect fuel economy?
A: Yes, incorrect temperature readings can lead to inefficient fuel combustion, affecting fuel economy.

Q: Is it necessary to replace the ECM if this fault code appears?
A: Not necessarily. Always verify sensor and wiring integrity before considering ECM replacement.

Q: Can this fault code cause the engine to overheat?
A: While not directly causing overheating, incorrect ambient temperature data can affect engine management, potentially leading to overheating under certain conditions.

Other FMI Codes for SPN 171