LT1 Scan: QDM Fault
Thread Starter
Racer
Joined: Jul 2006
Posts: 306
Likes: 1
From: StLouis, 93 Vert LT1
LT1 Scan: QDM Fault
Scanned 93 LT1 today with a Snap-On scanner, No codes,
everything else checks out ok but Im getting "QDM 2 and 3 faults",
QDM-1 is no fault however. The manual states that QDMs are
quad drivers? Can anyone offer any explanation on these?
everything else checks out ok but Im getting "QDM 2 and 3 faults",
QDM-1 is no fault however. The manual states that QDMs are
quad drivers? Can anyone offer any explanation on these?
Last edited by RetroTA; Aug 22, 2006 at 01:12 AM.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
The quad driver module in the ECM is used to control several high amperage devices such as cooling fans, A/C and torque convertor lockup clutches. It does so by providing a ground to the device relay terminals based on input to the ECM from switches and sensors.
My 93 also sets DTC 28 for Quad Driver Module circuit 3. I think it is caused by my aftermarket low temp fan switch installed in circuits 335 and 473, the same circuits controled by QDM circuit 3. Typically the manufacturer can provide no information. Hope that explanation helps.
My 93 also sets DTC 28 for Quad Driver Module circuit 3. I think it is caused by my aftermarket low temp fan switch installed in circuits 335 and 473, the same circuits controled by QDM circuit 3. Typically the manufacturer can provide no information. Hope that explanation helps.
Thread Starter
Racer
Joined: Jul 2006
Posts: 306
Likes: 1
From: StLouis, 93 Vert LT1
Thanks TopTech, I also saw another post from a member with a 93 whos
also getting the same faults on 2&3. The scanner manual says it doesnt necessarily mean somethings wrong and to consult the shop manual for
further reference. As of now Im not going to worry too much.
also getting the same faults on 2&3. The scanner manual says it doesnt necessarily mean somethings wrong and to consult the shop manual for
further reference. As of now Im not going to worry too much.
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
[QUOTE= I think it is caused by my aftermarket low temp fan switch installed in circuits 335 and 473, the same circuits controled by QDM circuit 3. QUOTE]
I remember reading this in the manual when I got the same error after installing an after market fan switch.
Larry
I remember reading this in the manual when I got the same error after installing an after market fan switch.
Larry
Melting Slicks
Joined: Feb 2005
Posts: 2,135
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From: Sebastian Florida
St. Jude Donor '06
It is also a sign, your ECM might be going south. Also, if you let the problem go to long. Your ECM will die, ask me how I know.
QDM 3 controls the Fan relays & A/C solenoid relay and somrthing else that I do not remember. Mine had a wire going to the solenoid that was bared in one spot.
QDM 3 controls the Fan relays & A/C solenoid relay and somrthing else that I do not remember. Mine had a wire going to the solenoid that was bared in one spot.
Last edited by Randy93; Aug 22, 2006 at 03:24 PM.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
[QUOTE=Vetracr]
I remember reading this in the manual when I got the same error after installing an after market fan switch.
Larry
Thanks Larry, the manufacturer of my switch didn't provide any such useful information but when I ran the diagnostic procedure for QDM-3 in the FSM I noticed immediatelly it was the same circuits controlled by the switch so I haven't let it concern me too much. I expect when the switch has grounded the circuit to operate the relay without the ECM commanding it the code is set though I haven't taken the time to verify.
Originally Posted by I think it is caused by my aftermarket low temp fan switch installed in circuits 335 and 473, the same circuits controled by QDM circuit 3. QUOTE
I remember reading this in the manual when I got the same error after installing an after market fan switch.
Larry
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
[QUOTE=toptechx6]
I expect when the switch has grounded the circuit to operate the relay without the ECM commanding it the code is set .
Thats exactly what happens. ECM checks for ground faults and sets code if found.
Larry
Originally Posted by Vetracr
I expect when the switch has grounded the circuit to operate the relay without the ECM commanding it the code is set .
Larry
