- Subject: Obtaining diagnostic service codes
- Units: Five-speeds
- Vehicle Application: Honda/Acura
- Essential Reading: Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
When an electrical failure or some type of system failure occurs, prompting the computer to initiate a programmed failsafe condition for the transmission, it is essential for the technician to have the ability to obtain the diagnostic service code that accompanies the failsafe condition. Not having the ability to obtain this code or codes in essence causes the technician to be blind.
Where does one begin diagnosing a problem with no idea where to start looking? Dropping the pan (if there is one to drop) to do a visual of the mechanical condition as well as a cursory overview of all related wiring is at best a beginning. But to know that one or more codes are stored yet not be able to obtain them with the shop’s scan tool raises the frustration level even higher.
Such a scenario seems to occur with Honda and Acura vehicles equipped with five-speed automatic transmissions. The D or D5 lamp will be blinking, indicating a code or codes are present, yet when the PCM is scanned for codes none are found.
Fortunately, Acura and Honda vehicles allow the technician to put the PCM into the Service Check Signal Mode by grounding terminal 1 or 9 in the OBD-II data-link connector (DLC). By doing so, the technician can flash out the “secret codes” lurking in the PCM.
In most instances there will be a brown wire in terminal 9. In other instances this wire will be in terminal 1, and terminal 9 will be empty (Figure 1). Once this wire is grounded and the ignition is turned to the on position with the engine off, codes can be retrieved via a flashing D/D5 lamp. The long flashes are the first digit of the code and the short flashes are the second digit. If a code below the number 10 is stored, it will be all short flashes.
The chart in Figure 2 provides the two-digit codes that can be obtained.
Two other points to mention here: If the MIL is illuminated, engine codes will always be displayed first, followed by the D/D5 light flashing the transmission codes stored.
Second, you may have noticed that the chart in Figure 2 has a third digit. Some scan tools have the ability to put the PCM into SCS mode through the tool itself. In these cases, the scan tool will display the two-digit trouble code as well as a third digit that indicates the nature of the failure, such as a circuit high or circuit low fault.