Diagnostic trouble codes - Revision history

Cliff at 18:35, 6 July 2026

2026-07-06T18:35:50Z

← Older revision		Revision as of 18:35, 6 July 2026
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	\| May indicate an internal ECM fault or related ECM problem.		\| May indicate an internal ECM fault or related ECM problem.
	\|}		\|}

			== Important note ==

			A trouble code does not automatically identify a failed part.

			For example, a sensor-related code may be caused by the sensor itself, but it may also be caused by wiring, connector corrosion, poor grounds, vacuum leaks, fuel pressure problems, exhaust leaks, or another condition that causes the ECM to see an unexpected signal.

			Trouble codes should be used as a starting point for diagnosis, not as a parts-replacement list.

	== Diagnosis ==		== Diagnosis ==

Cliff: /* Fiero trouble codes */

2026-07-06T18:35:21Z

Fiero trouble codes

@@ Line 27: / Line 27: @@
 Fiero ECM trouble codes commonly documented for stock 1984-1988 Fieros include:
-* [[Code 12]] - Diagnostic mode
+{| class="wikitable"
-* [[Code 13]] - Oxygen sensor circuit
+! Code
-* [[Code 14]] - Coolant temperature sensor circuit, high temperature indication
+! Description
-* [[Code 15]] - Coolant temperature sensor circuit, low temperature indication
+! Related system
-* [[Code 21]] - Throttle position sensor circuit, high voltage
+! Notes
-* [[Code 22]] - Throttle position sensor circuit, low voltage
+|-
-* [[Code 23]] - Manifold air temperature sensor circuit, low temperature indication
+| [[Code 12]]
-* [[Code 24]] - Vehicle speed sensor circuit
+| Diagnostic mode
-* [[Code 25]] - Manifold air temperature sensor circuit, high temperature indication
+| ECM
-* [[Code 32]] - EGR system
+| Code 12 indicates that the ECM is in diagnostic mode. It should flash first when codes are read through the ALDL connector.
-* [[Code 33]] - MAP sensor circuit, high voltage
+|-
-* [[Code 34]] - MAP sensor circuit, low voltage
+| [[Code 13]]
-* [[Code 35]] - Idle speed error
+| Oxygen sensor circuit
-* [[Code 42]] - Electronic spark timing circuit
+| Fuel control / emissions
-* [[Code 44]] - Lean exhaust indication
+| May relate to the oxygen sensor, wiring, connector, exhaust condition, or ECM signal interpretation.
-* [[Code 45]] - Rich exhaust indication
+|-
-* [[Code 51]] - PROM error
+| [[Code 14]]
-* [[Code 52]] - CALPAK error
+| Coolant temperature sensor circuit, high temperature indication
-* [[Code 53]] - System over-voltage
+| Engine control
-* [[Code 55]] - ECM error
+| May indicate a coolant temperature sensor circuit reading that appears too hot to the ECM.
 == Diagnosis ==

Cliff: /* Fiero trouble codes */

2026-07-06T10:47:42Z

Fiero trouble codes

← Older revision		Revision as of 10:47, 6 July 2026
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	== Fiero trouble codes ==		== Fiero trouble codes ==

	Fiero ECM trouble codes commonly documented for ~~the~~ 1984-1988 ~~cars~~ include:		Fiero ECM trouble codes commonly documented for stock 1984-1988 Fieros include:

	* [[Code 12]] - Diagnostic mode		* [[Code 12]] - Diagnostic mode
Line 40:		Line 40:
	* [[Code 34]] - MAP sensor circuit, low voltage		* [[Code 34]] - MAP sensor circuit, low voltage
	* [[Code 35]] - Idle speed error		* [[Code 35]] - Idle speed error
	* [[Code 41]] - Ignition reference or cam sensor circuit, depending on application
	* [[Code 42]] - Electronic spark timing circuit		* [[Code 42]] - Electronic spark timing circuit
	* [[Code 44]] - Lean exhaust indication		* [[Code 44]] - Lean exhaust indication

Cliff: /* Common Fiero trouble codes */

2026-07-06T10:45:53Z

Common Fiero trouble codes

← Older revision		Revision as of 10:45, 6 July 2026
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	* [[ECM diagnostic mode]]		* [[ECM diagnostic mode]]

	== ~~Common~~ Fiero trouble codes ==		== Fiero trouble codes ==

	~~Commonly discussed~~ Fiero ECM trouble codes include:		Fiero ECM trouble codes commonly documented for the 1984-1988 cars include:

	* [[Code 12]] - Diagnostic mode		* [[Code 12]] - Diagnostic mode
Line 33:		Line 33:
	* [[Code 21]] - Throttle position sensor circuit, high voltage		* [[Code 21]] - Throttle position sensor circuit, high voltage
	* [[Code 22]] - Throttle position sensor circuit, low voltage		* [[Code 22]] - Throttle position sensor circuit, low voltage
			* [[Code 23]] - Manifold air temperature sensor circuit, low temperature indication
	* [[Code 24]] - Vehicle speed sensor circuit		* [[Code 24]] - Vehicle speed sensor circuit
			* [[Code 25]] - Manifold air temperature sensor circuit, high temperature indication
	* [[Code 32]] - EGR system		* [[Code 32]] - EGR system
	* [[Code 33]] - MAP sensor circuit, high voltage		* [[Code 33]] - MAP sensor circuit, high voltage
	* [[Code 34]] - MAP sensor circuit, low voltage		* [[Code 34]] - MAP sensor circuit, low voltage
	* [[Code 35]] - Idle speed error		* [[Code 35]] - Idle speed error
			* [[Code 41]] - Ignition reference or cam sensor circuit, depending on application
	* [[Code 42]] - Electronic spark timing circuit		* [[Code 42]] - Electronic spark timing circuit
	* [[Code 44]] - Lean exhaust indication		* [[Code 44]] - Lean exhaust indication
	* [[Code 45]] - Rich exhaust indication		* [[Code 45]] - Rich exhaust indication
			* [[Code 51]] - PROM error
			* [[Code 52]] - CALPAK error
			* [[Code 53]] - System over-voltage
			* [[Code 55]] - ECM error

	== Diagnosis ==		== Diagnosis ==

Cliff: Created page with "'''Diagnostic trouble codes''' are fault codes stored by the ECM when the engine control system detects certain problems. On the Pontiac Fiero, trouble codes can be read through the ALDL diagnostic connector by placing the ECM into diagnostic mode and watching the check engine light flash the stored codes. == Overview == Fiero diagnostic trouble codes are not the same as modern OBD-II codes. They are earlier GM ECM trouble codes and are di..."

2026-07-06T10:41:18Z

Created page with "'''Diagnostic trouble codes''' are fault codes stored by the ECM when the engine control system detects certain problems. On the Pontiac Fiero, trouble codes can be read through the ALDL diagnostic connector by placing the ECM into diagnostic mode and watching the check engine light flash the stored codes. == Overview == Fiero diagnostic trouble codes are not the same as modern OBD-II codes. They are earlier GM ECM trouble codes and are di..."

New page

'''Diagnostic trouble codes''' are fault codes stored by the [[ECM]] when the engine control system detects certain problems.

On the [[Pontiac Fiero]], trouble codes can be read through the [[ALDL diagnostics|ALDL diagnostic connector]] by placing the ECM into diagnostic mode and watching the check engine light flash the stored codes.

== Overview ==

Fiero diagnostic trouble codes are not the same as modern OBD-II codes. They are earlier GM ECM trouble codes and are displayed as two-digit flash codes.

When the ECM is placed into diagnostic mode, the check engine light should flash [[Code 12]] first. Code 12 indicates that the ECM is operating in diagnostic mode. Stored trouble codes, if present, are then flashed after Code 12.

== Reading codes ==

Trouble codes are commonly read by jumpering the appropriate terminals on the ALDL connector, turning the ignition on without starting the engine, and counting the flashes of the check engine light.

Each code is flashed three times before moving to the next code.

Related topics:

* [[ALDL diagnostics]]
* [[ALDL connector]]
* [[Check engine light]]
* [[Code 12]]
* [[ECM diagnostic mode]]

== Common Fiero trouble codes ==

Commonly discussed Fiero ECM trouble codes include:

* [[Code 12]] - Diagnostic mode
* [[Code 13]] - Oxygen sensor circuit
* [[Code 14]] - Coolant temperature sensor circuit, high temperature indication
* [[Code 15]] - Coolant temperature sensor circuit, low temperature indication
* [[Code 21]] - Throttle position sensor circuit, high voltage
* [[Code 22]] - Throttle position sensor circuit, low voltage
* [[Code 24]] - Vehicle speed sensor circuit
* [[Code 32]] - EGR system
* [[Code 33]] - MAP sensor circuit, high voltage
* [[Code 34]] - MAP sensor circuit, low voltage
* [[Code 35]] - Idle speed error
* [[Code 42]] - Electronic spark timing circuit
* [[Code 44]] - Lean exhaust indication
* [[Code 45]] - Rich exhaust indication

== Diagnosis ==

A trouble code does not always mean that the named sensor or component is bad.

A code may be caused by wiring problems, connector corrosion, poor grounds, vacuum leaks, fuel pressure problems, mechanical problems, exhaust leaks, or other faults that cause the ECM to see an unexpected signal.

Before replacing parts, diagnosis should include inspection, basic testing, wiring checks, connector checks, and comparison with service information.

== Clearing codes ==

Stored trouble codes can be cleared after diagnosis and repair. The usual method is to disconnect ECM power long enough to erase stored memory.

After clearing codes, the vehicle may need to be driven again to see whether the code returns.

== See also ==

* [[ALDL diagnostics]]
* [[ECM]]
* [[Check engine light]]
* [[Electrical system]]
* [[Fuel system]]
* [[Engine]]
* [[Common problems]]

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