Reset ECU after disconnecting battery.
Thread Starter
6th Gear
Joined: May 2025
Posts: 6
Likes: 0
Reset ECU after disconnecting battery.
When I disconnect and then reconnect the battery on my 2005 if I don’t run it through a reset ride (drive it on the highway for 7 min let it decelerate, rinse later repeat) it throws codes within a week. Is there a way around this?
thanks!
thanks!
8th Gear
Joined: Jun 2025
Posts: 8
Likes: 2
From: Eastern Europe
ECM has nothing to do with the battery other than keeping fuel trims in its memory.
And not all ECMs store it in the RAM btw.
I've been using P01, P59, E38 and E40 ECMs in motorsport applications where you hit the kill switch after each run and battery disconnects from ECM, PDM and all other stuff - ECM has no power until the next start, those orange "12V Batt+" pins has no power as well due to race event regulations.
Had no problems with this kind of setups EVER so I think it's not the case.
And not all ECMs store it in the RAM btw.
I've been using P01, P59, E38 and E40 ECMs in motorsport applications where you hit the kill switch after each run and battery disconnects from ECM, PDM and all other stuff - ECM has no power until the next start, those orange "12V Batt+" pins has no power as well due to race event regulations.
Had no problems with this kind of setups EVER so I think it's not the case.
Thread Starter
6th Gear
Joined: May 2025
Posts: 6
Likes: 0
I’m sure most of you know more than I do about this and I appreciate your input and guidance! Thanks
To the question what codes.. the car goes into “low power” mode after a few days if I don’t do the reset run.
This is the procedure I used found in the forum.
Below was posted on this forum for the C5. Is anyone out there that can confirm it is the same for a C6? I was not aware of this happening when you disconnect the battery until a friend of mine replaced his battery just before getting a NC inspection in which it failed because a battery replacement requires a "driving cycle" before you can check the emissions.... 10 miles, 90 miles.. 10/20 restarts? Not a good thing when your tags expire in just a few days and apparently quite a few "cylces" are required for a vaild test.
++++++++++++++++++++++++++++++++++++++++ +++++++
Complete the GM drving cycle to reset your C5 computer.
General Motors' OBD-II driving cycle
• Cold Start. In order to be classified as a cold start, the engine coolant temperature must be
below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at start-up. Do not
leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
• Idle. The engine must be run for two and a half minutes with the air conditioner on and rear
defroster on. The more electrical load you can apply the better. This will test the O2 heater,
Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
• Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until
88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics
will be performed.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time
the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
• Decelerate. Let off the accelerator pedal. Do not shift or touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
• Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same
diagnostics as in step 3.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be
performed. If the catalyst is marginal or the battery has been disconnected, it may take 5
complete driving cycles to determine the state of the catalyst.
• Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or
brakes or shift gears.
To the question what codes.. the car goes into “low power” mode after a few days if I don’t do the reset run.
This is the procedure I used found in the forum.
Below was posted on this forum for the C5. Is anyone out there that can confirm it is the same for a C6? I was not aware of this happening when you disconnect the battery until a friend of mine replaced his battery just before getting a NC inspection in which it failed because a battery replacement requires a "driving cycle" before you can check the emissions.... 10 miles, 90 miles.. 10/20 restarts? Not a good thing when your tags expire in just a few days and apparently quite a few "cylces" are required for a vaild test.
++++++++++++++++++++++++++++++++++++++++ +++++++
Complete the GM drving cycle to reset your C5 computer.
General Motors' OBD-II driving cycle
• Cold Start. In order to be classified as a cold start, the engine coolant temperature must be
below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at start-up. Do not
leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
• Idle. The engine must be run for two and a half minutes with the air conditioner on and rear
defroster on. The more electrical load you can apply the better. This will test the O2 heater,
Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
• Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until
88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics
will be performed.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time
the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
• Decelerate. Let off the accelerator pedal. Do not shift or touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
• Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same
diagnostics as in step 3.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be
performed. If the catalyst is marginal or the battery has been disconnected, it may take 5
complete driving cycles to determine the state of the catalyst.
• Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or
brakes or shift gears.
