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Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » Why clear/reset DTC codes?

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Author Topic: Why clear/reset DTC codes?
soyjer
Member
Posts: 1
Post Why clear/reset DTC codes?
on: July 24, 2019 (GMT)

Is there any legitimate technical reason to ever manually reset/clear OBDII DTC trouble codes?

Don’t DTC’s eventually, after a few drive cycles, reset/clear themselves after the problem has been fixed?

I replaced my downstream O2 sensor to due to a P0138 code, and the check engine lamp shut off and full complete readiness was achieved after one short drive, but the P0138 still shows up under “Logged Faults”.

I want to pass the Basic CA smog test, and so, at this point, with full complete readiness achieved, am I better off just waiting for the PCM to reset/clear the code, or am I better off manually clearing the code and then having to start from scratch to achieve complete readiness?

I have seen varying answers elsewhere with regard to whether or not a logged code will fail a car even though the check engine light is off and complete readiness has been achieved, and so I am reluctant to take the car in for testing with the logged code still present, even though the check engine light is off and complete readiness has been achieved.

F-150Torqued
Member
Posts: 427
Post Re: Why clear/reset DTC codes?
on: July 24, 2019 (GMT)

I have long been an advocate of “NOT” clearing codes ‘indiscriminately’. I just adopted the reverse logic as you described – if the cause of the DTC is removed, the PCM will clear the light in a few drive cycles as you say (usually two, sometimes three). The light doesn’t hurt a thing – for most codes – Oil Pressure excepted. The advantage is you avoid the P1000 DTC and the delay – can actually be weeks or months for all readiness tests to complete. Especially since certain ones (EVAP monitor for example) will not run if IAT is > 95 degrees. Here in South Texas, that could be months in the summer time.

Although I do not have the problem, I would think if there is NO CEL, and Readiness indicates complete, the inspection will NOT fail based on existence of an old code. They should also be able to see the standard PID indicating number of miles driven with CEL ‘OFF’. (You got a receipt for the O2 sensor you can show them?).

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Capp777
Member
Posts: 2859
Post Re: Why clear/reset DTC codes?
on: July 24, 2019 (GMT)

How would you know when another new code
was presented during the time your check engine
lamp is left lit without reading DTCs?

F-150Torqued
Member
Posts: 427
Post Re: Why clear/reset DTC codes?
on: July 24, 2019 (GMT)

You don’t.

But frequently (though admittedly not ALWAYS), a CEL is accompanied by other codes. I can make the case that clearing codes obscures those from view until they return – in the same reverse fashion. It’s one of those arguments for which there is no clear winner on either side. I have just developed the attitude that (with the best code reader on the market), I can easily check them anytime. P1000 is one that I create myself, and I cannot clear it effectively.

So who is the winner?

I guess we need a CEL for each code!!!! LOL Our dash would look like one on an AirBus.

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moreause
Member
Posts: 509
Post Re: Why clear/reset DTC codes?
on: August 3, 2019 (GMT)

most of the check engine turn on immediately if a fault is detected

so doing a reset will confirm IMMEDIATELY if the issue is corrected , you don’t have to drive around not being sure the issue is solved

and you can detect the moment the issue happens by seeing the light going on

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