Code 15
Code 15 is a diagnostic trouble code related to the coolant temperature sensor circuit on the Pontiac Fiero.
Code 15 indicates that the ECM is seeing a coolant temperature sensor signal that represents an unusually low coolant temperature.
Overview
The coolant temperature sensor is a thermistor. Its resistance changes with temperature. As coolant temperature rises, sensor resistance decreases.
Code 15 is set when the ECM detects a high-voltage signal from the coolant temperature sensor circuit. To the ECM, this indicates an extremely low coolant temperature reading.
This can be caused by a faulty coolant temperature sensor, disconnected sensor, open circuit, poor connector contact, damaged wiring, or ECM input problem.
Flash pattern
Code 15 is displayed as:
- One flash
- Pause
- Five flashes
This represents code 15.
Animated flash pattern:
Meaning
Code 15 usually indicates that the ECM sees the coolant temperature sensor circuit as too cold.
Possible causes include:
- Disconnected coolant temperature sensor
- Faulty coolant temperature sensor
- Open circuit in the sensor wiring
- Poor connector contact
- Damaged wiring
- ECM input problem
Symptoms
Possible symptoms may include:
- Check engine light
- Rich fuel mixture
- Poor fuel economy
- Rough idle
- Hard starting
- Black exhaust smoke
- Poor drivability
- Cooling fan or temperature-related behavior affected by incorrect ECM temperature information
Diagnosis
Basic diagnostic checks include:
- Confirm that Code 15 is present.
- Inspect the coolant temperature sensor connector.
- Check whether the sensor is disconnected.
- Inspect the sensor wiring for damage or an open circuit.
- Check for corrosion or poor contact at the connector.
- Check for other stored trouble codes.
- Test the coolant temperature sensor resistance if equipment is available.
- Check ECM connector condition if the sensor and wiring appear correct.
Related codes
Related coolant-temperature and cooling-system topics include:
- Code 14 - Coolant temperature sensor circuit, high temperature indication
- Cooling system
- Overheating
- Air in cooling system
Notes
Code 15 does not usually mean the engine is actually too cold. It means the ECM is receiving a signal that appears too cold.
If the engine is fully warmed up but the ECM sees an extremely cold reading, the fuel mixture may become too rich.