Cliff: Created page with "'''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 E..."

2026-07-06T18:56:52Z

Created page with "'''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 E..."

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'''Code 15''' is a [[Diagnostic trouble codes|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:'''

[[File:Code15.gif|none]]

== 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.

== See also ==

* [[Diagnostic trouble codes]]
* [[ALDL diagnostics]]
* [[Coolant temperature sensor]]
* [[Cooling system]]
* [[Code 14]]
* [[ECM]]
* [[Electrical system]]

[[Category:Fieropedia]]
[[Category:Diagnostics]]
[[Category:Electrical system]]
[[Category:Cooling system]]
[[Category:Engine]]

Code 15 - Revision history