Cliff: Created page with "'''Code 23''' is a diagnostic trouble code related to the Manifold air temperature sensor circuit on the Pontiac Fiero. Code 23 indicates that the ECM is seeing a manifold air temperature sensor signal that represents an unusually low air temperature reading. == Overview == The manifold air temperature sensor, often abbreviated as MAT sensor, tells the ECM the temperature of the incoming air. The ECM uses this information for..."

2026-07-06T18:58:19Z

Created page with "'''Code 23''' is a diagnostic trouble code related to the Manifold air temperature sensor circuit on the Pontiac Fiero. Code 23 indicates that the ECM is seeing a manifold air temperature sensor signal that represents an unusually low air temperature reading. == Overview == The manifold air temperature sensor, often abbreviated as MAT sensor, tells the ECM the temperature of the incoming air. The ECM uses this information for..."

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'''Code 23''' is a [[Diagnostic trouble codes|diagnostic trouble code]] related to the [[Manifold air temperature sensor]] circuit on the [[Pontiac Fiero]].

Code 23 indicates that the [[ECM]] is seeing a manifold air temperature sensor signal that represents an unusually low air temperature reading.

== Overview ==

The manifold air temperature sensor, often abbreviated as MAT sensor, tells the ECM the temperature of the incoming air.

The ECM uses this information for fuel mixture calculations. If the ECM detects a manifold air temperature reading that is unusually low, it may set Code 23.

This can be caused by a faulty MAT sensor, disconnected sensor, wiring problem, connector problem, or ECM input problem.

== Flash pattern ==

Code 23 is displayed as:

* Two flashes
* Pause
* Three flashes

This represents code '''23'''.

'''Animated flash pattern:'''

[[File:Code23.gif|none]]

== Meaning ==

Code 23 usually indicates that the ECM sees the MAT sensor circuit as reading too cold.

Possible causes include:

* Disconnected MAT sensor
* Faulty MAT sensor
* MAT sensor wiring problem
* Poor connector contact
* Open circuit in the sensor wiring
* ECM input problem

== Symptoms ==

Possible symptoms may include:

* Check engine light
* Poor fuel economy
* Rich running
* Rough idle
* Hesitation
* Poor drivability
* Little or no obvious drivability problem

== Diagnosis ==

Basic diagnostic checks include:

# Confirm that Code 23 is present.
# Inspect the MAT 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 other stored trouble codes.
# Test the MAT sensor resistance if equipment is available.
# Check ECM connector condition if the sensor and wiring appear correct.

== Related codes ==

Related MAT sensor codes include:

* [[Code 25]] - Manifold air temperature sensor circuit, high temperature indication

== Notes ==

Code 23 does not usually mean the incoming air is actually extremely cold. It means the ECM is receiving a signal that appears too cold.

The MAT sensor and its wiring should be checked before replacing the sensor. Poor connections or broken wiring can cause the same code.

== See also ==

* [[Diagnostic trouble codes]]
* [[ALDL diagnostics]]
* [[Manifold air temperature sensor]]
* [[ECM]]
* [[Fuel system]]
* [[Electrical system]]
* [[Code 25]]

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

Code 23 - Revision history