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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1667
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2007 Yukon Denali. Check engine light while pulling a car

Customer Question

2007 Yukon Denali. Check engine light while pulling a car and trailer in the tow mode when braking and because of the tow mode decelerating. Code shows Radom misfire but engine runs smoothly and no detectable misfire. Cleared code and without hauling anything it set the code on down hill deceleration without being in the tow mode. No specific cylinder shown, just random misfire. Please help.
Submitted: 4 months ago.
Category: GMC
Expert:  xsvectOR replied 4 months ago.

can you monitor missfire counts on your scan tool?

Customer: replied 4 months ago.
scan tool counted thousands of misfires but it runs perfectly and no indication of misfiring
Expert:  xsvectOR replied 4 months ago.

on which cylinders?

Customer: replied 4 months ago.
Its random misfire. It does not identify any particular cylinder.
Expert:  xsvectOR replied 4 months ago.

you cannot monitor missfire counts on each cylinder with the scan tool?

Customer: replied 4 months ago.
It's random. The code is random misfire! This brand new 9000.00 scan tool displays random misfire. No specific cylinder is shown.
Expert:  xsvectOR replied 4 months ago.

what scan tool are you using? i understand what a random missfire means...po300 means more then 1 cylinder...you said you had thousands of miss fire counts...most good scan tools you can monitor each cylinder with a miss fire count... im not talking codes actual live data are you familiar??