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.
1993 Geo Prizm Base, StandardFACTORY OEM SERVICE PROCEDURE
CIRCUIT OPENING RELAY (PRIZM EXCEPT LSi)
- With ignition switch in ON position, momentarily backprobe ECM connector cavity A4 to ground using a fused jumper. If fuel pump runs, connect a DVOM from Data Link Connector (DLC) terminal FP to ground. See Fig 1 . If voltage measured while cranking is less than 10 volts, check for an open in Black wire between Clutch Pedal Position (CPP) switch, Park Neutral Position (PNP) switch and circuit opening relay or for an open in White/Black wire between circuit opening relay and ground. If circuit is okay, replace circuit opening relay and retest. If system still remains inoperative, replace ECM.
- If fuel pump does not run with cavity No. 4 jumpered to ground, momentarily jumper DLC terminal B+ to FP. If fuel pump runs, remove jumper from DLC. Backprobe circuit opening relay connector from cavity No. 2 to ground using a test light. If test light does not glow, repair open in Black/Red wire between fuse and relay box and circuit opening relay. If test light glows, turn ignition switch to LOCK position. Disconnect circuit opening relay connector. Connect a test light from circuit opening connector cavity No. 4 to B+. If test light glows while cranking, check for an open in Blue/Black wire between circuit opening relay and fuel sender assembly. If circuit is okay, replace circuit opening relay. If test light does not glow while cranking, check for an open in Green/Red wire between circuit opening relay and ECM. If circuit is okay, replace ECM.
- Remove jumper from DLC. Connect a test light from DLC terminal B+ to ground. If test light glows, backprobe fuel sender assembly connector from cavity No. 5 to B+ using test light. If test light glows, check for an open in Blue/Black wire between circuit opening relay, fuel sender assembly and DLC. If circuit is okay, replace fuel pump. If test light does not glow, check for poor ground. If ground is okay, repair open in White/Black wire between fuel sender assembly and ground. If test light does not glow when connected between B+ and ground, repair open in Black/Red wire between fuse and relay box, circuit opening relay and DLC.
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.