Coolant temperature sensor: Difference between revisions
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''Image wanted: ECM coolant temperature sensor location. Ideally include the 2.8L V6 sensor below the thermostat housing, screwed horizontally into the intake manifold water jacket, plus the 2.5L four-cylinder location near the thermostat housing.'' | |||
The ECM coolant temperature sensor location depends on the engine. | The ECM coolant temperature sensor location depends on the engine. | ||
Revision as of 19:16, 6 July 2026
Coolant temperature sensor refers to the engine coolant temperature sensor used by the Pontiac Fiero ECM.
The coolant temperature sensor tells the ECM how warm the engine is. The ECM uses this information for fuel mixture, idle control, cold-start enrichment, warm-up behavior, closed-loop operation, and diagnostic trouble code decisions.
Overview
The coolant temperature sensor is one of the most important engine-management sensors on the Fiero.
When the engine is cold, the ECM commands a richer fuel mixture and different idle behavior. As the engine warms up, the ECM gradually changes fuel and idle control based partly on the coolant temperature signal.
A faulty coolant temperature sensor or sensor circuit can cause poor starting, rough running, rich or lean operation, poor fuel economy, and trouble codes.
Location
Image wanted: ECM coolant temperature sensor location. Ideally include the 2.8L V6 sensor below the thermostat housing, screwed horizontally into the intake manifold water jacket, plus the 2.5L four-cylinder location near the thermostat housing.
The ECM coolant temperature sensor location depends on the engine.
On the 2.8L V6, the ECM coolant temperature sensor is located below the thermostat housing, screwed horizontally into the intake manifold water jacket.
On the 2.5L four-cylinder, the ECM coolant temperature sensor is located in the thermostat housing area.
This sensor should not be confused with the temperature gauge sender or the radiator fan switch. The Fiero uses separate temperature-related sensors and switches for different purposes.
The ECM coolant temperature sensor is the one used by the ECM for fuel mixture, idle behavior, warm-up operation, and diagnostic trouble codes such as Code 14 and Code 15.
Sensor operation
The coolant temperature sensor is a temperature-sensitive resistor. Its resistance changes as coolant temperature changes.
In general:
- Cold coolant produces a high-resistance signal.
- Hot coolant produces a low-resistance signal.
The ECM interprets this signal as engine temperature.
ECM sensor versus gauge sender
The coolant temperature sensor used by the ECM should not be confused with the coolant temperature sender used for the dashboard gauge or warning light.
The ECM coolant temperature sensor provides information to the ECM.
The gauge sender provides information to the instrument cluster.
A problem with the dashboard temperature gauge does not automatically mean the ECM coolant temperature sensor is faulty, and an ECM coolant temperature trouble code does not automatically mean the dashboard gauge sender is faulty.
Related topics:
Related trouble codes
Coolant-temperature-sensor-related diagnostic trouble codes include:
- Code 14 - Coolant temperature sensor circuit, high temperature indication
- Code 15 - Coolant temperature sensor circuit, low temperature indication
Code 14
Code 14 indicates that the ECM is seeing a coolant temperature sensor signal that represents an unusually high temperature reading.
Possible causes include:
- Actual overheating
- Faulty coolant temperature sensor
- Sensor wiring problem
- Poor connector contact
- Short to ground in the sensor circuit
- ECM input problem
Code 15
Code 15 indicates that the ECM is seeing a coolant temperature sensor signal that represents an unusually low temperature reading.
Possible causes include:
- Disconnected coolant temperature sensor
- Faulty coolant temperature sensor
- Sensor wiring problem
- Poor connector contact
- Open circuit in the sensor wiring
- ECM input problem
Symptoms
Possible symptoms of a coolant temperature sensor or circuit problem include:
- Check engine light
- Hard starting
- Rich running
- Poor fuel economy
- Black exhaust smoke
- Rough idle
- High idle
- Hesitation
- Stalling
- Poor cold-start behavior
- Poor warm-start behavior
- Cooling fan or temperature-related confusion during diagnosis
Diagnosis
Basic diagnostic checks include:
- Check for stored diagnostic trouble codes.
- Inspect the coolant temperature sensor connector.
- Check whether the sensor is disconnected.
- Inspect the sensor wiring for damage.
- Check for corrosion or poor contact at the connector.
- Check for actual overheating if Code 14 is present.
- Test sensor resistance if equipment and temperature-reference information are available.
- Compare ECM temperature data through ALDL diagnostics if live data is available.
- Check ECM connector condition if the sensor and wiring appear correct.
ALDL data
Live ECM data through ALDL diagnostics can be useful when diagnosing coolant temperature sensor problems.
If the ECM reports a coolant temperature that is obviously impossible, such as extremely cold when the engine is warm, or extremely hot immediately after a cold start, the sensor circuit should be checked.
This can help separate an actual cooling-system problem from an ECM sensor-input problem.
Cooling system relationship
The coolant temperature sensor reports engine temperature to the ECM, but it does not by itself prove whether the cooling system is working correctly.
If overheating is suspected, the cooling system should also be checked.
Related topics:
Notes
A coolant temperature sensor trouble code does not automatically mean the sensor itself has failed.
Wiring faults, poor connectors, open circuits, short circuits, ECM input problems, and actual overheating can all cause coolant-temperature-related codes.
Also make sure the ECM coolant temperature sensor is not confused with the dashboard temperature gauge sender.