Code 26, Quad-Driver Error, "N" Body: Notes

Control module controls most components with electronic switches, completing a ground circuit when actuated. These switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high, except for Torque Converter Clutch (TCC), which depends on brake switch and 2nd gear TCC switch.

QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A "Scan" tester displays status of each of these fault lines as "low equals okay" or "high equals fault".

Because of brake and 2nd gear switches in TCC circuit, Code 26 is set under different conditions for QDM "A" and QDM "B". Those conditions are as described:

QDM "A" fault line equals "high" for 20 seconds or more.
QDM "B" fault line equals "high" for 20 seconds or more and brake switch signal indicates switch is closed, 2nd gear switch indicates transaxle is in 2nd or 3rd gear or TCC is commanded on.

NOTE: QDM "B" fault line on A/T models will normally be "high" when vehicle is stopped. Control module ignores QDM "B" fault line except under conditions noted above.