ALDL diagnostics
ALDL diagnostics is an overview of Assembly Line Diagnostic Link diagnostic access on the Pontiac Fiero.
The Fiero uses a GM ALDL diagnostic connector that allows diagnostic trouble codes and engine control information to be accessed from the engine control system.
Overview
ALDL stands for Assembly Line Diagnostic Link. It was GM's diagnostic interface before modern OBD-II systems.
On the Fiero, the ALDL connector can be used to read diagnostic trouble codes, place the ECM into diagnostic mode, and, with suitable hardware and software, monitor available engine data.
ALDL connector
The ALDL connector is located inside the passenger compartment, under the trim plate near the cigarette lighter and center console area.
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Reading trouble codes
Trouble codes can be read by placing the ECM into diagnostic mode and watching the check engine light flash the stored codes.
This is commonly done by jumpering the appropriate terminals on the ALDL connector, then turning the ignition on without starting the engine.
The check engine light should flash Code 12 first. Code 12 indicates that the ECM is in diagnostic mode. Stored trouble codes, if present, are then flashed after Code 12.
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Live data
Some Fiero ECMs can provide live diagnostic data through the ALDL connector when used with compatible hardware and software.
Live data may include sensor readings and ECM information useful for diagnosing idle problems, fuel mixture problems, sensor faults, and drivability issues.
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Common diagnostic topics
- No-start diagnosis
- Idle problems
- Rich running
- Lean running
- Stalling
- Sensor diagnosis
- Ignition module failure
- Fuel pump problems
- Vacuum leaks
Limitations
ALDL diagnostics can help identify engine control problems, but trouble codes do not always identify the failed part directly.
A trouble code usually points to a circuit, sensor reading, or operating condition. Diagnosis should also include inspection, wiring checks, connector checks, ground checks, fuel pressure testing, ignition testing, vacuum leak testing, and service information.