HOW TO: Read DTC's (Diagnostic Trouble Codes)

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Pwnin O'Brien
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How To: Read DTC's (Diagnostic Trouble Codes)

Postby Pwnin O'Brien » Thu Apr 08, 2010 6:21 pm

Is your SERVICE ENGINE SOON lamp on and you don’t have an OBD-II reader or you don’t want to take your Pathfinder/QX4 to the dealer because you don’t want to pay the diagnostic fee? No Problem! The following tutorial will tell you how to read the DTC’s (Diagnotic Trouble Codes) from your vehicles ECM (engine control module) for free in only a matter of minutes.

When you start and drive your vehicle normally, the vehicles ECM is operating in what is called Diagnostic Test Mode I, it is constantly polling the various sensors and actuators to make sure everything is operating as it should. Once the ECM detects a problem with the vehicle, it will store a specific DTC that corresponds to that specific problem. After the ECM detects the problem for the first time, the SERVICE ENGINE SOON lamp will not illuminate (unless the DTC is for a misfire, three way catalyst function or closed loop control). However, if that same problem occurs the next time you drive the vehicle, the ECM will then illuminate the SERVICE ENGINE SOON lamp to let you know that there is a problem with your vehicle.

To figure out what is wrong with your vehicle you must first extract the DTC from the ECM so that you can begin troubleshooting the problem. Generally this task is done with an OBD-II reader which you plug into the OBD-II plug under the driver knee trim. If you were to take the vehicle to the dealership to extract the DTC they would hook your vehicle up to the CONSULT computer which would immediately tell them the DTC. The third method, which is explained below, is a DIY method which requires no tools and no expensive computers and can be done in your driveway.

1. Confirm that accelerator pedal is fully released, turn ignition switch “ON” (not starting vehicle) and wait 3 seconds.

2. Repeat the following procedure quickly five times within 5 seconds:

a) Fully depress the accelerator pedal.b) Fully release the accelerator pedal.

3. Count to 10 seconds, fully depress the accelerator pedal and keep it for approximately 10 seconds until the SERVICE ENGINE SOON lamp starts blinking.

4. Fully release the accelerator pedal.

The ECM has entered to Diagnostic Test Mode II (Self-diagnostic results).

Once the ECM has entered Diagnostic Test Mode II, it will immediately begin displaying the DTC’s via SERVICE ENGINE SOON lamp blinks. A particular trouble code can be identified by the number of four-digit numeral flashes. The “zero” is indicated by the number of ten flashes. The length of time the 1,000th-digit numeral flashes on and off is 1.2 seconds consisting of an ON (0.6-second) - OFF (0.6-second) cycle. The 100th-digit numeral and lower digit numerals consist of a 0.3-second ON and 0.3-second OFF cycle.

A change from one digit numeral to another occurs at an interval of 1.0-second OFF. In other words, the later numeral appears on the display 1.3 seconds after the former numeral has disappeared. A change from one trouble code to another occurs at an interval of 1.8-second OFF. In this way, all the detected malfunctions are classified by their DTC numbers. The DTC “0000” refers to no malfunction.

Below is an example of an ECM with two DTC’s stored, 1448 and 1110, respectively. Note the duration and separation of each SES blink.

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Pwnin O'Brien
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Re: How To: Read DTC's (Pwnin O'Brien)

Postby Pwnin O'Brien » Thu Apr 08, 2010 7:04 pm

The above procedure is only guaranteed to work on the later-model R50's. I will be modifying the thread to add the procedure for earlier-model R50's as well as R51's.

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Re: HOW TO: Read DTC's (Diagnostic Trouble Codes)

Postby Trisaurus » Thu Jun 27, 2013 4:42 pm

Is there an update to the above procedure list for R51's?

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Re: HOW TO: Read DTC's (Diagnostic Trouble Codes)

Postby Towncivilian » Thu Jun 27, 2013 6:10 pm

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