Rebuilding 93 C4,LT-! coupe, had engine running nice and smooth shut it down, came back about a week later-no go. engine turns fine but no start. check spark-fine nice and brite, must be fuel pump but no fuel pump is new, aha puter must be not letting fuel pump work, check codes, have code 28, book says "quad-drive module(qdm)#2 circuit or transaxle gear switch, probably 3rd gear switch circuit". Anybody know what it is or where in 'ell they put it?

 

http://forums.corvetteforum.com/c4-t...ad-driver.html
http://forums.corvetteforum.com/1554702604-post3.html

 

CIRCUIT DESCRIPTION
The ECM controls several components through the use of a "Quad-Driver" module integrated into the ECM. Most devices, such as solenoids or relays, receive battery power through a fused circuit to the ignition, and turn "ON", when the circuit is completed to ground. The "Quad-Driver" consists of several electronic switching circuits that provide the ground connection to complete these circuits and turn the devices "ON".

Each "Quad-Driver" has a fault line that is monitored by the ECM. When the QDM switch for a particular circuit is "OPEN", the voltage at the "sense line" will be high (near battery voltage), and when the device is turned "ON" (circuit completed to ground), the voltage at the "sense line" will drop to zero or near zero volts. When a device is commanded "OFF", the ECM expects the voltage in that "sense line" to be high, and when a device is commanded "ON", the ECM expects the voltage in that "sense line" to go low. The QDM fault detection circuit monitors the voltage in the sense line for each device controlled by the QDM. The ECM will monitor the voltage at the coolant fan and A/C clutch sense lines only when an A/C request signal is present. If the QDM fault detection circuit "sees" a voltage other than what it expects for a device in a particular "ON" or "OFF" state, the fault line status will change, and a Code 28 will set. The fault line signal status can be displayed on a "Scan" tool.

Code 28 will set if the ECM detects the wrong voltage potential in the QDM #3 fault line for 25 seconds. This code does not turn on the "Malfunction Indicator Light" (MIL, also known as the "Service Engine Soon" or SES light.)
QDM #3 is responsible for the cooling fans and the ac clutch. You have a short in one of those circuits.

 

I know that the quad drivers in a 1227165 will cause a fault if one of the circuits it is driving pulls too much current (shorted). The later ones may also do the same thing, I don't know.