Diagnostic mode?

**inaneninja** · 03-20-2004, 06:20 AM

i was telling ym friend i wanted to do an ODB hookup in my newly installed carPC but he cautioned me....

he seemed to think that on some newer cars (4-5 years and under) running ODB scans puts the ECU is some sorta of system test mode and makes your car retared.

i know people running older cars have said here on the forum that they have no problem, just wondering if anyone would con confirm / deny what i heard.

i got a 2001 dodge Dakota

**DavidL** · 03-20-2004, 02:00 PM

I assume your friend is probably talking about "limp mode" which is a default state that your truck would enter if it had a critical fault from unplugged sensor or sensor failure (not all sensors cause this condition). Simply plugging in an OBD2 hardware interface won't cause this problem. Of course, if the hardware or software isn't engineered well, it could create a fault condition, putting the vehicle into Limp.

Limp mode puts usually puts the ignition advance into a retarded condition which limits horsepower.

Now, if your interface box is pulling lots of parameters from the vehicle while the ECU is trying to manage the ignition / fuel / etc. systems, there is always the possibility that it can't "keep up" and have a misfire condition (intermittant). Similar to a video glitch running a new game software on an old PC with slow mhz.

**inaneninja** · 03-21-2004, 06:01 AM

thanks allot =D

**wi77iam** · 03-21-2004, 10:04 AM

Most of the software programs that come with the scanners allow you to reset the fault codes. So if there was some reading that caused the ECU to enter limp-home mode, and it was just an intermittent thing, you could potentially reset the ECU and get out of limp mode. Of course, if there was a real problem, the code should reappear.

I once had to drive 50 miles stuck in second gear because the stupid ECU went into limp mode for some glitch in the transmission that set its code. The dealer just reset the ECU and everything was fine but charged me $200.

Now I can reset the ECU myself and the scanner will pay for itself in one use. Leaving the scanner connected full time shouldn't affect anything either, unless as mentioned it induces a glitch in one of the other readings, which it shouldn't if designed properly.