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

The 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, the terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high, except for the Torque Converter Clutch (TCC), which depends on the 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, it would allow too much current into QDM. The QDM senses this and turns the output off, or its internal resistance increases to limit current flow and protect the QDM. The result is high output terminal voltage when it should be low. If the circuit from battery voltage or the component is open, or the 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 the presence of a current fault to control module's central processor. A "Scan" tester displays the status of each of these fault lines as "low equals okay" or "high equals fault".

Because of the brake and 2nd gear switches in the 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 an automatic transaxle vehicle will normally be "high" when the vehicle is stopped. The control module ignores the QDM B fault line except under conditions noted above.