Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Re: Quad driver diag code on 93 lt1
Quad drivers (QD) are integrated circuits inside the ECM that it uses to close or open the circuit path to ground, turning a device on or off (like your fans). Most quad driver circuit faults are due to a short in a device or its circuit. (Wiring/connectors). However at times a device or circuit that is open will set a quad driver fault code. Each quad driver can control up to four devices. So circuit diagrams will have to be used to find which devices the quad driver at fault is controlling.
A normally operating device and its circuit will have at least 20 ohms of resistance and can be checked with an ohmmeter. This will tell if the circuit or device is open however, this will not place the device in operation. So if the device is only failing due to heat after being in use for a period of time the fault will not be found with a resistance test.
If the vehicle is early gm and has a constant check engine light with a quad driver fault code set the computer (ECM) may have became permanently damaged. But if the ECM is replaced without any diagnosis to locate and repair the cause of the fault then the new ECM may soon become permanently damaged as well. On newer vehicles with an ECM that has protected quad drivers replacing the ECM is most often not necessary.
1969 Indy Pace Car
350/300HP RPO Z11
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.