P1599

DTC P1599 Cruise Power Management Diagnostic Chart:

Cruise Control Servo Wiring Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) controlled cruise system is designed to monitor itself to ensure that the desired cruise servo position and actual cruise servo position are equal to each other. If actual servo position is too high, the PCM will set Diagnostic Trouble Code (DTC) P1568, and the vehicle will operate in the "Power Management" mode. While in "Power Management," the PCM will shut off fuel to three cylinders to avoid overrevving the engine in case the throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo. DTC P1599 is an information code included to alert service that the vehicle has operated in the "Power Management" mode.

DTC P1599 WILL SET WHEN
Vehicle has operated in the "Power Management" mode.

ACTION TAKEN (PCM WILL DEFAULT TO)
A DTC P1599 set indicates that the vehicle has operated in "Power Management." While in "Power Management," the PCM shuts "OFF" fuel to 3 cylinders to avoid overrevving the engine in case the throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Most vacuum solenoids leak a small amount of vacuum when closed, but they should not leak enough to allow the servo to reach Wide Open Throttle (WOT) in 15 seconds with the vent solenoid closed.
2. When the vacuum solenoid is forced "ON," the vacuum will be vented unless the vent solenoid is stuck closed.

DIAGNOSTIC AIDS
A cruise control throttle cable which binds or intermittently sticks can cause the vehicle to operate in "Power Management" and DTC P1599 to set. DTC P1599 can also be set by manually compressing the cruise control servo to raise engine speed.

Outside interference such as a CB antenna lead near the PCM wiring harness may induce a false Servo Position Sensor (SPS) signal and set DTC P1599.