Check Engine Have the Codes Now What Do They Mean

[superrampie]

Hello

I have a 93 Grand AM SE with the 3.3L engine and have been able to pull some codes as the check engine light has come on.

The codes that I have are 26,27,31,43.

The engine has a very rough idle and it was at this time that the RPM drop almost to a stall and then came back up that the check engine light came on.

I have checked the error codes with the page here in the forum and still don't understand what is causing the errors and what needs to be done to fix the problem.

Thanks Matt

[xeroinfinity]

Welcome to AF !

Most ECM controlled devices are either solenoids or relays. Typically, solenoids are used for a circuit when the current draw is 0.75 amps or less, and relays are used in a circuit when the normal current draw is expected to exceed 0.75 amps. GM uses quad driver circuits inside the ECM to control the outputs to these devices.
So quad drivers (QD) are integrated circuits inside the ECM that it uses to close or open the circuit path to ground, turning the device on or off. Depending on the make and model year GM vehicles use different variations of quad drivers.

If your car has a constant check engine light with a quad driver fault code set the computer (ECM) may have became permanently damaged. So 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.

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.

Before replacing an ECM, always isolate the problem device or circuit. Replace the defective device or repair the circuit, and retest.

Each quad driver can control up to four devices. So diagrams will have to be used to find which devices the quad driver at fault is controlling

26 Quad Driver(QDM)Circuit
27 Quad Driver Module(QMD1)

31 PRNDL Error -- could be your Nuetral safty switch.
43 Knock Sensor(KS) Circuit - spark control - Probly your knock sensor is malfunctioning/bad.

So , you 31 & 43 could be very well why your getting the Quad driver code.

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.

With the proper test equipment it’s fairly easy to determine what circuit or device is causing a quad driver fault.

You will need a good digital multimeter and, if this first time buy the best would be one that has a 20 amp fused capability. The larger amp rating can come in handy when testing other electrical systems of your vehicle.
Also two 10 amp fused jumper wires keeping the in-line fuse as close to the power supply circuit as possible.

The most important thing to have on hand is information! The best would be the factory service manual but these are expensive. Or an online manual like AlldataDIY


Hope that helped,
and Good Hunting !