LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2001 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Fuel Systems >> Main Relay Circuit Diagnosis >> Metro
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Main Relay Circuit Diagnosis: Metro

  1. Perform diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in SELF-DIAGNOSTICS - METRO article. Repair any faults identified and go to next step.
  2. Check for an open IG-COIL fuse (15-amp) and/or FI fuse (15-amp). IG-COIL fuse (15-amp) is located in junction block under left side of instrument panel. FI fuse (15-amp) is located in fuse box. Fuse box is mounted on left inner side of fender on left side of engine compartment, behind relay box. If both fuses are okay, go to next step. If either fuse is open, go to step  13.
  3. Turn ignition on (engine off). Remove and reinstall main relay several times while listening for clicking sound of relay. Main relay is located in relay box. Relay box is located on left side of engine compartment, behind battery. If main relay does not click when being installed in relay box, go to next step. If main relay does click when being installed in relay box, condition may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - CARS article. Also check resistance of main relay and check for faulty electrical connections at PCM. Because temperature may affect fuel pump relay performance, allow vehicle to sit outside overnight and after running engine for 30 minutes.
  4. Turn ignition off. Remove main relay from relay box. Turn ignition on (engine off). Using a test light connected to ground, probe cavity No. 4 (White/Red wire) of main relay socket. See WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step  7.
  5. Using a test light connected to ground, probe cavity No. 1 (White/Red wire) of main relay socket. See WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step  7.
  6. Turn ignition off. Using a test light connected to battery voltage, probe cavity No. 2 (Light Blue/Black wire) of main relay socket. See WIRING DIAGRAMS article. Turn ignition on (engine off). If test light does not illuminate, go to step  8. If test light does illuminate, go to step  14.
  7. Locate and repair open circuit in White/Red wire between FI fuse (15-amp) and main relay. See WIRING DIAGRAMS article. After repair, go to step  16.
  8. Locate and repair open between cavity No. 2 (Light Blue/Black wire) of main relay socket and PCM connector C1 terminal No. 19 (Blue/Black wire). Light Blue/Black wire changes to Blue/Black wire at Black 16-pin in-line connector located at right rear side of engine compartment, near bulkhead. See WIRING DIAGRAMS article. See Figure. If an open does not exist, go to next step. If open was located and repaired, go to step  16.
  9. With ignition on, backprobe PCM connector C3 terminal No. 20 (Black/White wire) with a test light connected to ground. See Figure. If test light does not illuminate, go to next step. If test light does illuminate, go to step  11.
  10. Locate and repair open in Black/White wire between IG-COIL fuse (15-amp) and PCM connector C3 terminal No. 20. After repair, go to step  16.
  11. Turn ignition off. Disconnect PCM connector C1. Using a test light connected to battery voltage, probe harness side of PCM connector C1 terminals No. 1 (Black/Green wire), No. 13 (Black/Blue wire) and No. 26 (Black/Red wire). If test light does not illuminate at any ground terminal, go to next step. If test light does illuminate at all ground terminals, go to step  15.
  12. Locate and repair all identified opens in ground circuits (Black/Green, Black/Blue and Black/Red wires) between PCM connector C1 and ground point. Ground point is located at left end of cylinder head. After repair, go to step  16.
  13. Locate and repair short to ground in IG-COIL fuse (15-amp) circuit (Black/White wire) from junction block to PCM connector C3 and fuel pump relay in relay box. Also locate and repair short to ground in FI fuse (15-amp) circuit (White/Red wire) from fuse box to main relay in relay box. See WIRING DIAGRAMS article. After repair, go to step  16.
  14. Replace main relay. After repair, go to step  16.
  15. Replace PCM. After repair, reprogram PCM and go to next step. See PROGRAMMING in SELF-DIAGNOSTICS - METRO article.
  16. Operate vehicle under same conditions as recorded for original symptom. If system operates properly without setting any trouble codes, system is okay at this time. If system does not operate properly and trouble codes are not set, check main relay resistance and faulty electrical connections at PCM connectors. Because temperature may affect main relay performance, allow vehicle to sit outside overnight and after running engine for 30 minutes. See SYSTEM & COMPONENT TESTING - CARS - METRO & PRIZM article. If system does not operate properly and trouble codes are set, diagnose and repair trouble code. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - METRO article.
scientia non olet · About LEMON Manuals