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Reading ECU Fault Codes

< RomRaider and Reflashing FAQ | | Subaru specific trouble codes >

Introduction

This technical article describes how to read the current and historic fault codes stored within your ECU. The following procedures for reading fault codes vary from model year and the information you require.

  • Reading ECU Codes Via OBDII - For all Impreza's, both current and historical ECU fault codes can be displayed using diagnostics software connected to your OBDII connector.
  • Manually Reading ECU Codes - On Classic shape Impreza's only (not Newage) faults can be displayed manually as pulses of the Check Engine Light.

You may also be interested in Subaru specific trouble codes or generic OBDII trouble codes which are described on separate pages.

Reading ECU Codes Via OBDII

A number different tools, both commercial and open source, are available to read ECU fault codes via the ODBII diagnostics connector. What follows is a description of reading ECU fault codes for Newage Impreza's using ecuExplorer which, at the time of writing, is distributed free by TARI Racing. This software is described in more detail in the ECU diagnostics and data logging technical article.

  1. Download and install the latest release of ecuExplorer
  2. Connect up to the OBDII diagnostics port with reference to the connecting to your ECU technical article.
  3. Turn on your ignition
  4. Invoke ecuExplorer and select the Trouble Code Reader option from the left-hand tree view.
  5. Current and historic fault codes will be displayed as illustrated in the figure below.

Figure 1 - ecuExplorer CEL Codes on Newage

In the above figure two historic fault codes are displayed. The owner of this Newage Impreza has a decat downpipe causing fault code P0420, and hit fuel cut on an early winter morning when using a Dawes manual boost controller causing fault code P0244.

Manually Reading ECU Codes (Classic Impreza's only)

On Classic shape Impreza's only (not Newage) faults can be displayed as pulses of the Check Engine Light. If the Check Engine Light goes out there is no fault.

In order to perform diagnostic (and ECU resets) you will need to connect some wires together under your steering column. Note, the following procedure only works for Classic shape Impreza's, not for Newage.

  • Make sure your ignition is OFF
  • Connect the Black 'Read Memory' connectors together as illustrated below.

Figure 1 - Black and Green Connectors on Classic Impreza

When the above are connected you are in diagnostics mode. Turn your ignition ON and 'read' the ECU code(s) being reported according to the following instructions. Note, you may here relays clicking and your fan starting and stopping - this is normal when in diagnostics mode.

In Diagnostic Mode No Fault is indicated by the Check Engine Light continuously & evenly flashing on/off (this is also used to indicate the successful completion of an ECU Reset).


Figure 2 - Check Engine Light Pulse Width

The long pulses (1.3 Seconds) indicate Tens and the short pulses (0.2 Seconds) indicate ones. Pulses are separated by Short Pauses (0.2 Seconds), multiple codes are separated by a Long Pause (1.8 Seconds).

The simplest way for an inexperienced mechanic to retrieve codes is to write the codes down in a sort of Morse Code (dots and dashes), and start a new line when you get a 1.8 Second pause (for NEW code), and then add the actual numbers up after code retrieval is completed.

(See Example Below)

--- CODE EXAMPLE, SINGLE CODE ---

1.3 second pulse (10)
0.2 second pause
1.3 second pulse (10....for a total of 20)
0.2 second pause
0.2 second pulse (1.....for a total of 21)
0.2 second pause
0.2 second pulse (1.....for a total of 22)
0.2 second pause
0.2 second pulse (1.....for a total of 23)
(Code 23 -- MAF Sensor)

--- CODE EXAMPLE, MULTIPLE CODE ---

1.3 second pulse (10)
0.2 second pause
1.3 second pulse (10....for a total of 20)
0.2 second pause
0.2 second pulse (1.....for a total of 21)
0.2 second pause
0.2 second pulse (1.....for a total of 22)
0.2 second pause
0.2 second pulse (1.....for a total of 23)
1.8 second pause (this means NEW code)

1.3 second pulse (10)
0.2 second pause
0.2 second pulse (1.....for a total of 11)
0.2 second pause
.2 second pulse (1.....for a total of 12)
(Codes 23 and 12, MAF Sensor and Starter Circuit)

Impreza Fault Codes

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Page last modified on September 13, 2008, at 10:02 AM
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