2008 Honda S2000 BaseFACTORY OEM SERVICE PROCEDURE

Alternator FR Signal Circuit Troubleshooting

  1. Start the engine, and let it idle.
  2. Monitor the ALTERNATOR in the DATA LIST with the HDS.
  3. Check if the indicated percentage varies when the headlight switch is on.

    Does the percentage vary? 

    1. YES  - The alternator signal circuit is OK.
    2. NO  - Go to step  4.
  4. Turn the headlight switch and ignition switch OFF.
  5. Disconnect the alternator 4P connector.
  6. Turn the ignition switch ON (II).
  7. Measure voltage between ECM connector terminals A9 and B13.

    Is there about 5 V? 

    1. YES  - Go to step  8.
    2. NO  - Go to step  13.
      Fig 1: Measuring Voltage Between ECM Connector Terminals A9 & B13
      G03693208Courtesy of AMERICAN HONDA MOTOR CO., INC.
  8. Turn the ignition switch OFF.
  9. Jump the SCS line with the HDS.
  10. Disconnect ECM connector B (24P).
  11. Connect alternator 4P connector terminal No. 4 to body ground with a jumper wire.
    Fig 2: Connecting Alternator 4P Connector Terminal No. 4 To Body Ground With Jumper Wire
    G03693209Courtesy of AMERICAN HONDA MOTOR CO., INC.
  12. Check for continuity between body ground and ECM connector terminal B13.

    Is there continuity? 

    1. YES  - Test the alternator (see ALTERNATOR AND REGULATOR CIRCUIT TROUBLESHOOTING ).
    2. NO  - Repair open in the wire between the ECM (B13) and the alternator.
      3. Fig 3: Checking Continuity Between Body Ground & ECM Connector Terminal B13
      G03693210Courtesy of AMERICAN HONDA MOTOR CO., INC.
  13. Turn the ignition switch OFF.
  14. Jump the SCS line with the HDS.
  15. Disconnect ECM connector B (24P).
  16. Check for continuity between body ground and ECM connector terminal B13.

    Is there continuity? 

    1. YES  - Repair short in the wire between the ECM (B13) and the alternator.
    2. NO  - Update the ECM if it does not have the latest software, or substitute a known-good ECM (see UPDATING THE ECM ), then recheck. If the symptom/ indication goes away with a known-good ECM, replace the original ECM (see ECM REPLACEMENT ).
    Fig 4: Checking Continuity Between Body Ground & ECM Connector Terminal B13
    G03693211Courtesy of AMERICAN HONDA MOTOR CO., INC.
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.