Technical How To
Got a Check Engine Light (CEL)?
K-Series.com Staff
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Got CEL?
How to Read Diagnostic Trouble Codes (DTCs)
without an OBDII Scan Tool
- by rsxmachine
1. Malfunction Indicator Lamp (MIL) aka Check-Engine Light (CEL) comes on while engine is running -- this indicates something is wrong and the ECU has stored a Diagnostic Trouble Code (DTC).
2. Turn the engine OFF. Locate the OBDII Data Link Connector (DLC) under the driver's side dash (in the RSX, it is in the vicinity of your right knee when you are driving). Use a jumper wire to connect terminals 4 and 9 of the DLC. IMPORTANT: Make sure you are connecting only the correct terminals as shown, otherwise you risk causing electrical damage to the ECU!
3. Turn the ignition key to the ON (II) position, but do not start the engine.
4. Carefully observe the CEL. It will flash in a distinct manner to display any DTCs that are stored (if there are no codes stored, the CEL will not flash). The pattern of flashes indicates a one- or two-digit numeric code. The first digit of the code is represented by long flashes. The second digit of the code is represented by short flashes. A zero is represented by a brief pause. For example, four long flashes followed by five short flashes is code 45. One long flash followed by a pause is code 10.
5. If there is more than one DTC stored, the CEL will display them in sequence, then it will continue to repeat all the codes after they have been displayed one time. Record and double-check all codes displayed.
6. Look up the meaning of the codes retrieved on the DTC Index Page. (Note that the one- or two-digit CEL codes correspond to more detailed four-digit OBDII codes.)
7. Clearing the codes: if you wish to clear the stored DTCs and reset the ECU, remove the #6 fuse (15A) in the underhood fusebox for at least 10 seconds. However, if you are going to take your vehicle to a professional mechanic for repair, it's better to leave the DTCs in the ECU so that they can read and troubleshoot them with an OBDII scan tool or Honda PGM console.
[TBA later: Automatic Transmission DTC Index, ABS DTC Index]
To test this procedure I disconnected the intake air temperature sensor and one of the camshaft position sensors on my RSX, then ran the engine until the CEL came on. Reading the CEL flashes with the above method, I retrieved codes 10 and 57. As can be seen on the DTC Index Page these correspond to problems with the Intake Air Temperature (IAT) Sensor and the Camshaft Position (CMP) Sensor, respectively. To verify these I then plugged in my Auterra OBDII scan tool and retrieved the DTCs P0113 (IAT Sensor Circuit High Voltage) and P0340 (CMP Sensor No Signal).
