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.
Main Relay (Computer/Fuel System): Testing and Inspection
2004 Honda S2000 L4-2.2LSECTION Testing and Inspection
PGM-FI Main Relay Circuit Troubleshooting
1. Turn the ignition switch OFF, then disconnect the PGM-FI main relay 7P connector.
2. Check for continuity between body ground and PGM-FI main relay 7P connector terminal No. 3.
Is there continuity?
YES - Go to step 3.
NO - Repair open in the wire between the PGM-FI main relay and G101.
3. Measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 7.
Is there battery voltage?
YES - Go to step 5.
NO - Go to step 4.
4. Check for a blown ACGS (15 A) fuse in the under-hood fuse/relay box.
Is the fuse blown?
YES - Repair the short in the wire between the PGM-FI main relay and the ACGS (15 A) fuse.
NO - Repair the open in the wire between the PGM-FI main relay and the ACGS (15 A)fuse.
5. Turn the ignition switch ON (II), and measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 5.
Is there battery voltage?
YES - Go to step 7.
NO - Go to step 6.
6. Check for a blown No. 2 FUEL PUMP SRS (15 A) fuse in the under-dash fuse/relay box.
Is the fuse blown?
YES - Repair short in the wire between the PGM-FI main relay and the No. 2 FUEL PUMP SRS (15 A) fuse.
NO - Repair open in the wire between the PGM-FI main relay and the No. 2 FUEL PUMP SRS (15 A) fuse.
7. Push the clutch pedal in, then turn the ignition switch ON (II), and press the engine start button. Measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 2.
Is there battery voltage?
YES - Go to step 9.
NO - Go to step 8.
8. Check for a blown No. 21 STARTER SIGNAL (7.5 A) fuse in the under-dash fuse/relay box.
Is the fuse blown?
YES - Repair short in the wire between the PGM-FI main relay and the No. 21 STARTER SIGNAL (7.5 A) fuse.
NO - Repair open in the wire between the PGM-FI main relay and the No. 21 STARTER SIGNAL (7.5 A).
9. Turn the ignition switch OFF. and disconnect ECM connector A (32P).
10. Check for continuity between PGM-FI main relay 7P connector terminal No. 1 and ECM connector terminal A15.
Is there continuity?
YES - Go to step 11.
NO - Repair open in the wire between the PGM-FI main relay and the ECM (A15).
11. Reconnect ECM connector A (32P) and the PGM-FI main relay 7P connector.
12. Turn the ignition switch ON (II), and measure voltage between ECM connector terminals B1 and B20, and between B9 and B20 individually.
Is there battery voltage?
YES - Go to step13.
NO - Check for an open in the wires between the PGM-FI main relay and the ECM (B1, B9). If the wires are OK, replace the PGM-FI main relay.
13. Turn the ignition switch OFF, then ON (II) again, and measure voltage between ECM connector terminals A15 and B2 within the first 2 seconds after the ignition switch is turned ON (II).
Is there 1.0 V or less?
YES - The PGM-FI main relay may be faulty; go to STEP 14.
NO - Substitute a known-good ECM and recheck. If the voltage is now normal, replace the original ECM.
14. Remove the PGM-FI main relay.
15. Connect battery power to PGM-FI main relay 7P connector terminal No. 2 and connect ground to the PGM-FI main relay 7P connector terminal No. 1. Then check for continuity between PGM-FI main relay 7P connector terminals No. 5 and No. 4.
NOTE: Use the terminal numbers shown. Ignore the terminal numbers molded into the relay.
Is there continuity?
YES - Go to step 16.
NO - Replace the PGM-FI main relay and recheck the circuit.
16. Connect battery power to PGM-FI main relay 7P connector terminal No. 5, and connect ground to PGM-FI main relay 7P connector terminal No. 3. Then check for continuity between PGM-FI main relay 7P connector terminals No. 7 and No. 6.
Is there continuity?
YES - Go to step 17.
NO - Replace the PGM-FI main relay and recheck the circuit.
17. Connect battery power to PGM-FI main relay 7P connector terminal No. 6, and connect ground to PGM-FI main relay 7P connector terminal No. 1. Then check for continuity between PGM-FI main relay 7P connector terminals No. 5 and No. 4.
Is there continuity?
YES - The PGM-FI main relay is OK.
NO - Replace the PGM-FI main relay and recheck the circuit.
1. Turn the ignition switch OFF, then disconnect the PGM-FI main relay 7P connector.
2. Check for continuity between body ground and PGM-FI main relay 7P connector terminal No. 3.
Is there continuity?
YES - Go to step 3.
NO - Repair open in the wire between the PGM-FI main relay and G101.
3. Measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 7.
Is there battery voltage?
YES - Go to step 5.
NO - Go to step 4.
4. Check for a blown ACGS (15 A) fuse in the under-hood fuse/relay box.
Is the fuse blown?
YES - Repair the short in the wire between the PGM-FI main relay and the ACGS (15 A) fuse.
NO - Repair the open in the wire between the PGM-FI main relay and the ACGS (15 A)fuse.
5. Turn the ignition switch ON (II), and measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 5.
Is there battery voltage?
YES - Go to step 7.
NO - Go to step 6.
6. Check for a blown No. 2 FUEL PUMP SRS (15 A) fuse in the under-dash fuse/relay box.
Is the fuse blown?
YES - Repair short in the wire between the PGM-FI main relay and the No. 2 FUEL PUMP SRS (15 A) fuse.
NO - Repair open in the wire between the PGM-FI main relay and the No. 2 FUEL PUMP SRS (15 A) fuse.
7. Push the clutch pedal in, then turn the ignition switch ON (II), and press the engine start button. Measure voltage between body ground and PGM-FI main relay 7P connector terminal No. 2.
Is there battery voltage?
YES - Go to step 9.
NO - Go to step 8.
8. Check for a blown No. 21 STARTER SIGNAL (7.5 A) fuse in the under-dash fuse/relay box.
Is the fuse blown?
YES - Repair short in the wire between the PGM-FI main relay and the No. 21 STARTER SIGNAL (7.5 A) fuse.
NO - Repair open in the wire between the PGM-FI main relay and the No. 21 STARTER SIGNAL (7.5 A).
9. Turn the ignition switch OFF. and disconnect ECM connector A (32P).
10. Check for continuity between PGM-FI main relay 7P connector terminal No. 1 and ECM connector terminal A15.
Is there continuity?
YES - Go to step 11.
NO - Repair open in the wire between the PGM-FI main relay and the ECM (A15).
11. Reconnect ECM connector A (32P) and the PGM-FI main relay 7P connector.
12. Turn the ignition switch ON (II), and measure voltage between ECM connector terminals B1 and B20, and between B9 and B20 individually.
Is there battery voltage?
YES - Go to step13.
NO - Check for an open in the wires between the PGM-FI main relay and the ECM (B1, B9). If the wires are OK, replace the PGM-FI main relay.
13. Turn the ignition switch OFF, then ON (II) again, and measure voltage between ECM connector terminals A15 and B2 within the first 2 seconds after the ignition switch is turned ON (II).
Is there 1.0 V or less?
YES - The PGM-FI main relay may be faulty; go to STEP 14.
NO - Substitute a known-good ECM and recheck. If the voltage is now normal, replace the original ECM.
14. Remove the PGM-FI main relay.
15. Connect battery power to PGM-FI main relay 7P connector terminal No. 2 and connect ground to the PGM-FI main relay 7P connector terminal No. 1. Then check for continuity between PGM-FI main relay 7P connector terminals No. 5 and No. 4.
NOTE: Use the terminal numbers shown. Ignore the terminal numbers molded into the relay.
Is there continuity?
YES - Go to step 16.
NO - Replace the PGM-FI main relay and recheck the circuit.
16. Connect battery power to PGM-FI main relay 7P connector terminal No. 5, and connect ground to PGM-FI main relay 7P connector terminal No. 3. Then check for continuity between PGM-FI main relay 7P connector terminals No. 7 and No. 6.
Is there continuity?
YES - Go to step 17.
NO - Replace the PGM-FI main relay and recheck the circuit.
17. Connect battery power to PGM-FI main relay 7P connector terminal No. 6, and connect ground to PGM-FI main relay 7P connector terminal No. 1. Then check for continuity between PGM-FI main relay 7P connector terminals No. 5 and No. 4.
Is there continuity?
YES - The PGM-FI main relay is OK.
NO - Replace the PGM-FI main relay and recheck the circuit.
RENDER: 1.0x
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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.