Honda Accord/Prelude 1984-1995 Repair Guide

System Diagnosis

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READING CODES



When the "Check Engine" warning light on the dashboard comes on and stays on, it indicates a problem in the fuel injection/emissions system. Check the ECU for fault codes. On certain models, some codes will not trigger the check engine light; if driveability has suffered, check for stored fault codes.

The most common error when using fault codes is to assume the indicated component has failed rather than checking the entire circuit. The presence of a trouble code means simply that the electrical circuit for the named component is not functioning properly. For example, a code for the oxygen sensor circuit does not automatically mean the oxygen sensor has failed. A wire terminal may simply be loose or corroded at the connector. When using diagnostic or fault codes, always remember that the entire circuit including the component must be checked carefully.

Carbureted Models

See Figure 1

Although the 1984-89 Accords and 1984-87 Preludes use a feedback control ECU, the control unit does not have a self-diagnostic capability. If a fault occurs in a circuit, careful diagnosis and testing of the individual components must be used to find the problem. A thorough understanding of electronic systems is required.

Beginning with the 1988 Preludes, the control unit or ECU includes self-diagnostic capabilities similar to those found on fuel injected models. Codes 1 through 9 are indicated by a series of short flashes; two-digit codes use a long flash for the first digit followed by the appropriate number of short flashes. For example, Code 14 would be indicated by 1 long flash followed by 4 short flashes. Codes are separated by a pause between displays. Multiple codes are transmitted in an alternating pattern. For example, a code 3 and 14 would be displayed as 3 short flashes (for Code 3) followed by the separator pause, then 1 long flash and 4 short flashes (for Code 14).

  1. The ECU is located on the front floor, about under the passenger's toes. Pull the carpet down; a large protective cover will be seen over the ECU. On the upper edge of the cover is a window or opening, allowing the Light Emitting Diode (LED) to be viewed.
  2.  
  3. Turn the ignition ON , but do not start the engine. The LED should begin to flash.
  4.  

In the event that a code is encountered which is not on the chart, re-count the number of flashes. If the code is truly wrong, it will be necessary to swap the ECU for a known-good unit and recheck. Since this can be expensive, you may wish to bring the car to a reputable repair facility if no other cause of the failure can be found. This may save you the expense of purchasing an unnecessary part.

  1. Once the codes are read, refer to the appropriate troubleshooting chart for testing procedures. Note that some tests will require the Honda test harness. (Use harness No. 07HAZ-PJ7010A and 07HAZ-PH7000A for 1988-89 and 07LAJ-PT30100 for 1990). This is a device which allows safe testing of the electrical circuits without backprobing connectors. It installs between the ECU and the wiring harnesses. This is a specialty item, usually only available from dealers.
  2.  



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Fig. Fig. 1: The test harness allows for safe diagnosis of the electrical circuits without backprobing connectors

1988-90 PRELUDE FAULT CODES PGM-CARB SYSTEM


CODE 1: Oxygen content
 
CODE 2: Vehicle speed pulser
 
CODE 3: MAP sensor, electrical signal
 
CODE 4: Vacuum switch signal
 
CODE 5: MAP sensor, vacuum signal
 
CODE 6: Coolant temperature
 
CODE 7: Clutch switch signal (manual trans.)
 
CODE 7: Shift position signal (auto trans.)
 
CODE 8: Ignition coil signal
 
CODE 10: Intake air temperature
 
CODE 14: Electronic Air Control Valve (EACV)
 

Fuel Injected Models
1985 ACCORD

See Figures 2 and 3

On the 1985 Accord, there are four LEDs. They are part of the ECU, which is located under the passenger's seat, and are numbered 1, 2, 4 and 8 (as counted from right to left). The codes are interpreted by comparing the display on the ECU to the display pattern shown in the chart.



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Fig. Fig. 2: ECU fault code display for the 1985 Accord

  1. Access the ECU.
  2.  
  3. Turn the ignition switch ON ; the LEDs will display any stored codes in a pattern.
  4.  

In the event that a code is encountered which is not on the chart, re-count the number of flashes. If the code is truly wrong, it will be necessary to swap the ECU for a known-good unit and recheck. Since this can be expensive, you may wish to bring the car to a reputable repair facility if no other cause of the failure can be found. This may save you the expense of purchasing an unnecessary part.

  1. If no codes are displayed but a driveablity problem exits, testing of the individual components of the system is necessary to find the problem. If codes are displayed, follow the appropriate troubleshooting chart in this section.
  2.  



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Fig. Fig. 3: Display code chart for the 1985 Accord

1986-89 ACCORD AND 1985-91 PRELUDE

See Figures 4, 5 and 6

On 1986-89 Accord and 1985-91 Prelude models, there is only one LED display. The LED will blink to indicate the trouble code. The ECU is located under the driver's seat on the Accord. On 1985-87 Preludes, it is in the left side trim panel beside the rear seat. On 1988-91 Preludes, it is located under the carpet on the right front passenger footwell.

Codes 1 through 9 are indicated by a series of short flashes; two-digit codes use a long flash for the first digit followed by the appropriate number of short flashes. For example, Code 14 would be indicated by 1 long flash followed by 4 short flashes. Codes are separated by a pause between displays. Multiple codes are transmitted in an alternating pattern. For example, a code 3 and 14 would be displayed as 3 short flashes (for Code 3) followed by the separator pause, then 1 long flash and 4 short flashes (for Code 14).



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Fig. Fig. 4: Reading fault codes from the LED display on the ECU



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Fig. Fig. 5: Fault code chart for 1986-89 Accord and 1985-89 Prelude

  1. Access the ECU.
  2.  
  3. Turn the ignition switch ON ; the LED will display any stored codes by rhythmic flashing.
  4.  

In the event that a code is encountered which is not on the chart, re-count the number of flashes. If the code is truly wrong, it will be necessary to swap the ECU for a known-good unit and recheck. Since this can be expensive, you may wish to bring the car to a reputable repair facility if no other cause of the failure can be found. This may save you the expense of purchasing an unnecessary part.

  1. If no codes are displayed but a driveablity problem exits, testing of the individual components of the system is necessary to find the problem. If codes are displayed, follow the appropriate troubleshooting chart in this section.
  2.  



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Fig. Fig. 6: Fault code chart for 1990-91 Prelude. The single asterisk applies to 2.0L engines only; a double asterisk pertains only to the 2.1L engine

1990-95 FOUR CYLINDER ACCORD AND 1992-95 PRELUDE

See Figures 7, 8, 9, 10, 11 and 12

On 1990-95 Accord (except V-6) and 1992-95 Prelude, the codes are read from the check engine light after the two-wire service connector has been jumpered. On Accords, the service connector is under the dash on the passenger side. On Preludes, it is located behind the center console. Codes 1 through 9 are indicated by a series of short flashes; two-digit codes use a long flash for the first digit followed by the appropriate number of short flashes. For example, Code 14 would be indicated by 1 long flash followed by 4 short flashes. Codes are separated by a pause between displays. Multiple codes are transmitted in an alternating pattern. For example, a code 3 and 14 would be displayed as 3 short flashes (for Code 3) followed by the separator pause, then 1 long flash and 4 short flashes (for Code 14).



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Fig. Fig. 7: Fault codes are read from the check engine light on most late-model vehicles



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Fig. Fig. 8: On Accords, the service connector is located under the dash on the passenger side



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Fig. Fig. 9: The service connector on Preludes is located behind the center console

  1. Use a jumper wire to connect the two terminals of the service connector together.
  2.  
  3. Turn the ignition switch ON ; the check engine light will display any stored codes by rhythmic flashing.
  4.  

In the event that a code is encountered which is not on the chart, re-count the number of flashes. If the code is truly wrong, it will be necessary to swap the ECU for a known-good unit and recheck. Since this can be expensive, you may wish to bring the car to a reputable repair facility if no other cause of the failure can be found. This may save you the expense of purchasing an unnecessary part.

  1. If no codes are displayed but a driveablity problem exits, testing of the system individual components is necessary to find the problem. If codes are displayed, follow the appropriate troubleshooting chart in this section.
  2.  



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Fig. Fig. 10: Fault code chart for 1990-93 Accords



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Fig. Fig. 11: Fault code chart for 1994-95 Accords (four cylinder)



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Fig. Fig. 12: Fault code chart for 1992-95 Preludes

1995 ACCORD V-6

See Figure 13

On the 1995 Accord V-6, the fault codes can only be read using an OBD-II compliant scan tool or Honda's PGM tester. Follow the instructions supplied by the scan tool manufacturer. The service connector for the scan tool is located behind the ashtray in the center console.



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Fig. Fig. 13: On 1995 Accords equipped with the V-6 engine, fault codes can only be read using an OBD-II compliant scan tool or Honda's PGM tester. Note that the service connector is located behind the ashtray in the center console

CLEARING CODES




WARNING
Before disconnecting power from the ECU, ALWAYS make sure the ignition switch is in the OFF position. Failure to do so may result in a voltage spike damaging the ECU. This can be a very expensive component to replace.

Stored codes are erased from memory by disconnecting power to the ECU for at least 30 seconds. Disconnecting the negative battery cable will clear the memory of the ECU, as well as other solid-state equipment such as the radio. Keep a record of the station pre-sets and any applicable security codes. The ECU may also be cleared by pulling the appropriate fuse from the underhood fuse and relay box. This may be the BACK-UP, CLOCK or CLOCK/RADIO fuse.

 
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