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OBD II Reader question

 
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Old 11 Jan 2018, 11:53 am
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Default OBD II Reader question

Used my OBD II scan tool to clear the MIL light after taking care of a bad thermostat.

As soon as I plugged in the tool it came on and let me read the two codes, both P0128 for bad thermostat temp and bad engine temp. I then cleared the codes and everything is back to normal.

At no time did I have the key in the 'on' position, the key was in my pocket.

Looking at the booklet that came with the scanner this a.m. it states that the unit should be plugged in and the key set to the 'on' position. Engine running or not does not seem to matter.

My question is did I screw up? Should the scanner have worked at all without the key being in the 'on' position? Is being in the 'on' position just for additional readings to be looked for?

It's an Autel MS309 aka Handy's choice.
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Old 11 Jan 2018, 12:16 pm
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Default Re: OBD II Reader question

Usually you should do this with the key in the on position but with the engine not running. On some cars the readers do seem to work with the key off. If me, I'd just check it again with the key on. If the codes are gone, they were likely erased the first time.
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Old 11 Jan 2018, 01:12 pm
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Default Re: OBD II Reader question

Scan tools must first "WAKE UP" (so to say) the ECM. You must have the key at least in the "on" position. Not sure if I agree with run for many reason but I saw your scan tool said either or.

Although on some ECMs (Not the PT's PCM) you can access some but not all the ECU "secrets" (operating information) with "no" key actuation. This is not really a good way to do any OBDII diagnostic work.

As an example I use a Ultra Gauge, on a few of my cars it will see and read only 30 area's of operation with simply accessing the OBDII diagnostic connector. However if I turn the key to "on" it will access all the available cells which is from 60 to 90+ area's of the ECU. I can not successfully reset the monitors without the key in the "on" position as I am pretty sure it is with most all ECU's?
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Old 11 Jan 2018, 01:30 pm
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Default Re: OBD II Reader question

Quote:
Originally Posted by NitroPT View Post
Scan tools must first "WAKE UP" (so to say) the ECM. You must have the key at least in the "on" position. Not sure if I agree with run for many reason but I saw your scan tool said either or.

Although on some ECMs (Not the PT's PCM) you can access some but not all the ECU "secrets" (operating information) with "no" key actuation. This is not really a good way to do any OBDII diagnostic work.

As an example I use a Ultra Gauge, on a few of my cars it will see and read only 30 area's of operation with simply accessing the OBDII diagnostic connector. However if I turn the key to "on" it will access all the available cells which is from 60 to 90+ area's of the ECU. I can not successfully reset the monitors without the key in the "on" position as I am pretty sure it is with most all ECU's?
These pictures show the UG reading ECU (not PT Cruiser PCM) with no key "ON" and then key "ON"

Key is OFF
20180111_101437_resize.jpg

20180111_101439_resize.jpg

20180111_101442_resize.jpg

Key is OFF
20180111_101456_resize.jpg


Key is ON
20180111_101523_resize.jpg
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Old 11 Jan 2018, 02:21 pm
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Default Re: OBD II Reader question

Thanks, boys!

As Handy suggested I just went out and plugged it in, it came on as soon as it was plugged in and I pressed enter, it did its scan then went to the menu screen.

I then exited and unplugged it, re-plugged it in and when the opening screen came on I turned the key to the on position, I did not start the car.

This time the scan was noticeably longer before going to the menu screen.

However, the codes had cleared so at least that worked.

NitroPT you're probably correct in that without the key being on it was not reading everything it could.

Unfortunately, do to age and some physical problems I'm not able to do much work myself anymore, however, I still like to learn and have a bit of a high I.Q. and even though it seems you two can't agree on if water is wet or not, I, for one, want to let you both know how much I appreciate your sharing of knowledge with the rest of us mere mortals.

Thank you both.
Darrin
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Old 11 Jan 2018, 02:34 pm
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Default Re: OBD II Reader question

It is more likely that when you changed the parts correcting the problem starting the engine, the PCM ran through the cycle and deactivated the DTC.

The end result is everything seems to be corrected.
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Old 11 Jan 2018, 03:38 pm
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Default Re: OBD II Reader question

Not really certain of that, the MIL light remained on with the associated ding for a couple of days until I cleared the codes.

Then again, it took a couple of days after I noticed it was running cold before the light came on, it may just have taken a couple of days for it to realize it was fixed, also.

But, as you say, it all worked out in the end!
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