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Pulling Codes and Clearing the Computer Without a Reader

Mechanic (stock clipart)

There are a lot of things you’ll need to do to repair a vehicle. One of those will be pulling OBD II codes from the computer as part of the diagnosis process and clearing that computer in order to see if new codes come up. Sometimes, a reader isn’t handy. For those times, there are options.

To begin with, anyone who plans to work on vehicles regularly should have an OBD reader. They are relatively low-cost and readily available. Readers that can pull codes and clear them are commonly sold in auto parts stores, tool outlets, and online. For simple mechanics’ work, a pocket reader that uses your smartphone for output is ideal and easy to use. These can be had for less than $50 from many sources.

When a reader isn’t handy, though, there are alternatives. Grab a paper and pencil and be ready to do a lot of writing and (likely) some page-flipping or Googling. Obviously the vehicle to be tested requires some battery power for the procedure to work.

Turn the key on - not to start, just the “on” position - then quickly off, back on, off, on, off, on, and off. Do this within five seconds. The sequence should be On-Off-On-Off-On-Off-On. Leave the key in the “on” position and wait. The engine error code light should begin to blink. It’s blinking will indicate the error code(s) stored in the computer.

The two-digit flashes will have a short pause between each digit followed by a longer pause before the next set of digits are flashed. So an error code 0401 would look like the light coming on steady, then turning off with a pause, then flashing four times. Then a long pause followed by another steady on, off with a pause, and single flash. This can be recorded and searched as error code P0401.

This process does not clear the car’s computer, so the codes can be replayed as needed. When you’re ready to reset the computer to clear those codes, disconnect all power from the car’s systems, wait, then re-start (re-attach the power). This is usually done by disconnecting the negative battery cable, then the positive cable, and tying those cables together. Waiting a few minutes usually clears any power remaining. Hooking the battery back up restarts the computer.