Diagnostic Overview

TEMP SENSOR ECU DIAGNOSTICS: 

• Circuit Fault Diagnostics:  With a normally functioning sensor that has no circuit issues, the signal voltage should never read 5.0 volts or 0.0 volts. This allows the module the capability of diagnosing an open or short in the sensor or wiring. As a general rule, a voltage reading above approximately 4.9 volts will typically set a circuit high/open fault. A voltage below approximately 0.10 volts will typically set a circuit Low fault. Calibrated thresholds can vary slightly from module to module and vehicle to vehicle.
• Performance Fault Diagnostics:  Added resistance in the sensor or circuitry can cause an irrational reading and no circuit fault. The module will check the signal for a plausible reading in most cases. This can be done using different methods. One common way is by comparing the sensor reading to other temperature sensors. With this method the module will compare the sensors at a time when the readings should be within a calibrated threshold of each other (Ex. Ignition on after a cold soak). Another method could be to monitor for the temperature to increase or decrease when turning on or off a device that is being controlled by the ECU. In either case, an irrational reading can set a sensor performance fault.