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.
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HOMESERVICE MANUALSGEO1993PRIZM L4-1600CC 1.6L DOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONINITIAL INSPECTION AND DIAGNOSTIC OVERVIEWINTERMITTENT MALFUNCTIONS
1993 Geo Prizm L4-1600cc 1.6L DOHC
Intermittent Malfunctions
1993 Geo Prizm L4-1600cc 1.6L DOHCSECTION Intermittent Malfunctions
INTERMITTENTS
Definition: Problem may or may not light the MIL or store a DTC.
DO NOT use the diagnostic trouble code (DTC) charts for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of DTC charts may result in replacement of good parts.
^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform visual/physical checks. Check for:
- Poor mating of the connector halves or terminal not fully seated in the connector body (backed out).
- Improperly formed or damaged terminal. All connector terminals in the problem circuit should be carefully reformed or replaced to insure proper contact tension.
- Poor terminal-to-wire connection. This requires removing the terminal from the connector body to check.
^ If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a digital multimeter connected to a suspected circuit. An abnormal voltage reading, when the problem occurs, indicates the problem may be in that circuit.
^ An intermittent MIL with no stored DTC may be caused by:
- MIL wire to ECM/PCM shorted to ground.
- Diagnostic request terminal wire to ECM/PCM shorted to ground.
- ECM/PCM grounds refer to ECM/PCM wiring diagrams.
^ Check for electrical system interfence caused by a defective relay, ECM/PCM driven component, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.
^ Check for improper installation of electrical options such as lights, two-way radios, etc.
^ Ignition wires should be routed away from spark plug wires. distributor wires, distributor housing, coil and generator.
Definition: Problem may or may not light the MIL or store a DTC.
DO NOT use the diagnostic trouble code (DTC) charts for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of DTC charts may result in replacement of good parts.
^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform visual/physical checks. Check for:
- Poor mating of the connector halves or terminal not fully seated in the connector body (backed out).
- Improperly formed or damaged terminal. All connector terminals in the problem circuit should be carefully reformed or replaced to insure proper contact tension.
- Poor terminal-to-wire connection. This requires removing the terminal from the connector body to check.
^ If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a digital multimeter connected to a suspected circuit. An abnormal voltage reading, when the problem occurs, indicates the problem may be in that circuit.
^ An intermittent MIL with no stored DTC may be caused by:
- MIL wire to ECM/PCM shorted to ground.
- Diagnostic request terminal wire to ECM/PCM shorted to ground.
- ECM/PCM grounds refer to ECM/PCM wiring diagrams.
^ Check for electrical system interfence caused by a defective relay, ECM/PCM driven component, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.
^ Check for improper installation of electrical options such as lights, two-way radios, etc.
^ Ignition wires should be routed away from spark plug wires. distributor wires, distributor housing, coil and generator.
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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.