SonicVQ

After reading a few posts about resetting the ECM by disconnecting the battery, I wanted to explain why you shouldn't.

When you reset the ECM this way, not only are you erasing the codes, but also the "freeze frame" (aka mode $02) which is a snap shot of all the cars sensors at the time the CEL came on.(engine speed, engine temp, throttle position, intake manifold pressure, vehicle speed, etc) This is VERY valuable diagnostic information.

You are erasing the "mode $06" test results. Many components are tested while the car is being driven and the test results are stored in mode $06. This is also a VERY valuable diagnostic tool. Did you know that in this mode there is a cylinder misfire counter for EACH cylinder? Would that be helpful to track down a stumble?

You are also resetting all of the "readiness monitors" which means you will fail any emissions or I/M test as it takes time for all the monitors to be set. (even when following the steps of the proper drive cycle)

Did you know that once a problem is fixed, the check engine light will turn off after the car has been driven 3 times without the a error/issue being detected?

In the past when ECMs were much simpler, it was a good idea. Today's ECMs are very complex and there is no need. Resetting the ECM can make it take longer to fix an issue and erases valuable troubleshooting information.

socketz67

Is this info also lost when you perform a soft reset like this?
I had a CEL come on a week or so and the car was running fine, so I thought that it may be the infamous gas cap issue, so I performed a reset like the one in the video (took a few attempts to get the timing down) and the code went away and has since not returned.

SonicVQ

After scrubbing the FSM, that video shows most of the "IDLE AIR VOLUME LEARNING" procedure which is on page EC 648.

Generally any time the check engine light is turned off/reset the diagnostic data is erased.

With a $15 OBD scanner like ELM327 that uses wi-fi and a $10 app (OBD Fusion or Torque) it may be best to read the actual code, compared to blindly reseting it hoping it doesn't come back.

Starting next month, I will be creating a series of videos on youtube that explain how to use and understand OBD-II. I think a lot of people will be able to benefit from this.

justinc7100

I just had my transmission fluid changed by Inifniti at 100k. Since the transmission adapts to the old fluid should I reset my ECU so it adapts to the thinner fluid so it does not damage the clutch?

G37sGraphite

iTrader: (9)

Your talking about resetting due to a CEL?
I unplugged my battery completely for over 14 hours getting a new battery...and the windows did not even need to be reinitialized. Radio presets not erased... Is this normal?
I wonder if that is the case if all the other data your saying is actually lost or not....?

SonicVQ

Good question!
(1) The automatic transmission is not controlled by the ECM. It is controlled by the TCM (transmission control module)

(2) Our automatic transmission uses temperature and pressure sensors to determine how and when it shifts. It is very smart and automatically adjusts to the condions.

Sooooo, there is no need. Drive and enjoy your G

SonicVQ

The data that is lost is the data stored in the ECM and is engine related.

Radio stations and window positions are stored on other modules. Window position is probably the BCM (body control module). I don't know where the radio stations are stored.

blnewt

iTrader: (13)

Good stuff Sonic! Look forward to your youtube clips, be sure to post a link on the site