Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1989 Geo Metro BaseFACTORY OEM SERVICE PROCEDURE
Retrieving Codes
- Perform DIAGNOSTIC CIRCUIT CHECK before diagnosing vehicle using self-diagnostic system. See DIAGNOSTIC CIRCUIT CHECK chart in this article.
- Trouble code(s) can be retrieved through either one of the 2 diagnostic switch terminals. See Fig 1 . One is located in the monitor connector in engine compartment and the other one is in the fuse block, located in the passenger compartment.
- To retrieve code(s) using the diagnostic terminal in fuse block, insert spare fuse into diagnostic switch terminal. The ECM will toggle the CHECK ENGINE light, flashing code(s).
- To retrieve code(s) using the monitor connector in the engine compartment, ground terminal "B" (diagnostic switch terminal) of connector. The ECM will then output self-diagnostic code(s). Both these diagnostic terminals, when grounded, sets the ignition timing to base timing.
- If no trouble codes exist, the ECM will flash Code 12. If trouble codes are stored, the lowest numbered code will be given first. Each code will be displayed 3 times. Proceed to CODE CHARTS for diagnosing stored codes.
TROUBLE CODE IDENTIFICATION CHART
| Code | Circuit Affected | Probable Cause | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 12 | System Is Normal | - | ||||||||
| 13 | Oxygen Sensor | Open Circuit | ||||||||
| 14 | Coolant Temp. Sensor | High Temp. Indicated | ||||||||
| 15 | Coolant Temp. Sensor | Low Temp. Indicated | ||||||||
| 21 (1) | Throttle Switch | Both Idle Switch Throttle Switch ON | ||||||||
| 21 (2) | Throttle Position Sensor | Signal Voltage High | ||||||||
| 22 (2) | Throttle Position Sensor | Signal Voltage Low | ||||||||
| 23 | Manifold Air Temp. Sensor | Low Temp. Indicated | ||||||||
| 24 | Vehicle Speed Sensor | No Speedometer | ||||||||
| 25 | Manifold Air Temperature | High Temp. Indicated | ||||||||
| 31 | MAP Sensor | Signal Voltage Low With High Vacuum | ||||||||
| 32 | MAP Sensor | Signal Voltage High With Low Vacuum | ||||||||
| 41 | Ignition Signal | No Signal | ||||||||
| 42 (3) | Crank Angle Sensor | No Signal For 2 Seconds | ||||||||
| 51 (4) | EGR System | EGR VSV Inoperative | ||||||||
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Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.