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Jim Grant's Tech Tips
‘92 Saturn SL, Quad Driver Code
Q: My ‘92 Saturn SL 1.9L SOHC TBI check engine code shows a quad driver module problem. The Saturn dealer says the Quad driver is inside the computer. Luckily, a friend has an identical Saturn. We swapped computers, but the problem did not move to his car, and my car still has the same fault with his computer, What gives!
- Larry McNeely
A:
Just because you have a Quad driver code doesn’t mean the Quad driver is bad. All a Quad driver code means is that an expected value is not present when it’s suppose to be. Also a Quad driver is a techy name for 4 on-off switches arranged in a group, hence the name Quad driver. The computer watches the voltage values on each switch and knows that if the switch is on, a voltage value will be seen. When the switch is off the opposite voltage value will be seen. Simply put, light on, light off. So what can set a quad driver code? You’d be surprised. How about a bad bulb? How about a bad fuse? The answer is yes to both questions. Yes, a bad bulb or failed fuse can set a Quad driver code. Start with checking your fuses. There can be up to 3 fuses that supply power to circuits controlled by the Quad drivers. If the fuses are good the next check would be of all or some of the following, depending on how your vehicle is equipped: Up shift light bulb, coolant hot bulb, shift to drive bulb, A/C relay, coolant fan relay, EGR solenoid, Canister Purge solenoid, even a speedometer output signal goes to one of the switches on the Quad driver. I guess what I’m saying is, that it is unlikely you have a computer problem. It’s more likely that the Quad driver code is present because the computer is not seeing the information that it expects to see at one of the switches.
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