How to Troubleshoot Fuel and Emissions Systems

Intermittent Failures

The term ‘‘intermittent failure'' means a system may have had a failure, but it checks OK now. If the Malfunction Indicator Lamp (MIL) on the dash does not come on, check for poor connections or loose wires at all connectors related to the circuit that you are troubleshooting.

Opens and Shorts

‘‘Open'' and ‘‘Short'' are common electrical terms. An open is a break in a wire or at a connection. A short is an accidental connection of a wire to ground or to another wire. In simple electronics, this usually means something won't work at all. In complex electronics (like ECM's/PCM's) this can sometimes mean something works, but not the way it's supposed to.

How to Use the Honda PGM Tester or a Scan Tool

If the MIL has come on

1.Start the engine and check the MIL.


2.If the MIL stays on, connect the Honda PGM Tester (A) or a scan tool to the Data Link Connector (DLC) (B) located under the driver's side of the dashboard.


3.Turn the ignition switch ON (II).

4.Check the Diagnostic Trouble Code (DTC) and note it. Also check the freeze frame data. Refer to the DTC Troubleshooting Index and begin the appropriate troubleshooting procedure.

  • Freeze frame data indicates the engine conditions when the first malfunction, misfire or fuel trim malfunction was detected.
  • The scan tool and the Honda PGM Tester can read the DTC, freeze frame data, current data, and other Engine Control Module (ECM)/Powertrain Control Module (PCM) data.
  • For specific operations, refer to the user's manual that came with the scan tool or Honda PGM Tester.

If the MIL did not come on

If the MIL did not come on but there is a driveability problem, do the Symptom Troubleshooting.

If you can't duplicate the DTC

Some of the troubleshooting requires you to reset the ECM/PCM and try to duplicate the DTC. If the problem is intermittent and you can't duplicate the code, do not continue through the procedure. To do so will only result in confusion and, possibly, a needlessly replaced ECM/PCM.

How to Reset the ECM/PCM

You can reset the ECM/PCM in either of two ways:

NOTE: After resetting the ECM/PCM, do the ECM/PCM idle learn procedure.

Reset the ECM/PCM with the scan tool or Honda PGM Tester

1.Turn the ignition switch ON (II). Do not start the engine.

2.Use the scan tool or Honda PGM Tester to clear the DTC.

NOTE: For specific operations, refer to use's manual that came with the with the scan tool or Honda PGM Tester.

Reset the ECM/PCM removing the fuse

1.Turn the ignition switch OFF.

2.Remove the No. 20 (15A) fuse (A) from the under-dash fuse/relay box (B) for 60 secons.


How to End a Troubleshooting Session (required after any troubleshooting)

1.Reset the ECM/PCM as described above.

2.Turn the ignition switch OFF.

3.Disconnect the scan tool or Honda PGM Tester from the DLC.

  • The ECM is part of the immobilizer system. If you replace the ECM/PCM, it will have a different immobilizer code. In order for the engine to start, you must rewrite the immobilizer code with the Honda PGM Tester.
  • Do the idle learn procedure

How to Remove the ECM/PCM for Testing

If the inspection for a trouble code requires voltage or resistance checks at the ECM/PCM connectors, remove the ECM/PCM and test it:

1.Remove the passenger's dashboard under cover (A), side kick panel (B) and glove box inner case.


2.Disconnect the connectors (C), and remove the bols, then remove the ECM/PCM (D).

3.Do the idle learn procedure.

How to Troubleshoot Circuits at the ECM/PCM

1.Gently slide the sharp tester probe (A) into the connector from wire side until it touches the end of the wire terminal.


2.If you cannot get to the wire side of the connector or the wire side is sealed (A), disconnect the connector and probe the terminals (B) from the terminal side. Do not force the probe into the connector.

Do not puncture the insulation on a wire.Punctures can cause poor or intermittent electrical connections.


ECM/PCM Updating and Substitution for Testing

Special Tools Required
Honda Interface Module ( (HIM) EQS05A35570)

Use this procedure when you have to substitute a known-good ECM/PCM in a troubleshooting procedure. Update the ECM/PCM only if the ECM/PCM does not already have the latest software loaded.

NOTE: Do not turn the ignition switch OFF while updating the ECM/PCM. If you turn the ignition switch OFF, the ECM/PCM can be damaged.

How to Update the ECM/PCM

  • To ensure the latest program is installed, do an ECM/PCM update whenever the ECM/PCM is substituted or replaced.
  • You cannot update an ECM/PCM with the program it already has. It will only accept a new program.
  • Before you update the ECM/PCM, make sure the vehicle's battery is fully charged.
  • To prevent ECM/PCM damage, do not operate anything electrical (audio system, brakes, A/C, power windows, door locks, etc.) during the update.
  • If you need to diagnose the Honda Interface Module (HIM) because the HIM's red (#3) light came on or was flashing during the update, leave the ignition switch in the ON (II) position when you disconnect the HIM from the data link connector (DLC). This will prevent ECM/PCM damage.

1.Turn the ignition switch ON (II). Do not start the engine.

2.Connect the Honda Interface Module (HIM) to the data link connector (DLC) (A) located under the driver's side of dashboard.


3.Do the ECM/PCM update procedure as described on the HIM label and in the ECM/PCM update system. If the software in the ECM/PCM is the latest, replace the ECM/PCM.

How to Substitute the ECM/PCM

1.Remove the ECM/PCM from the vehicle.

2.Install a known-good ECM/PCM in the vehicle.

3.Rewrite the immobilizer code with the ECM/PCM replacement procedure in the Honda PGM Tester: It allows you to start the engine.

4.After completing your tests, reinstall the original ECM/PCM and rewrite the immobilizer code with the ECM/PCM replacement procedure in the Honda PGM Tester again.

5.Do the idle learn procedure.