P1850

Schematic:

Circuit Description with 4L30-E Automatic Transmission
The band apply solenoid assembly is attached in the valve body in the main case of the transmission. The solenoid controls transmission fluid flow to the band servo. The TCM controls the solenoid with a Pulse Width Modulated (PWM) signal. The signal frequency is approximately 32 Hz. The duty cycle is controllable from 0-100 percent.

The Band Apply Solenoid receives supply power via the Transmission Power Relay (internal to the TCM). The TCM controls the solenoid by grounding the control circuit via an internal solid state device called a driver. The driver has a fault line which is monitored by the TCM. When the TCM is commanding a component ON, the voltage of the control circuit should be low (near 0 volts). When the TCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high (near system voltage).

When the TCM detects a continuous open, short to power, short to ground in the band control solenoid circuit or the band control solenoid assembly, the DTC P1850 sets. DTC P1850 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
The ignition switch is in the RUN position.

The TCM high side driver is closed.

CONDITIONS FOR SETTING THE DTC
DTC P1850 sets if any one of the following conditions occurs in 0.18 seconds.
^ The band control solenoid assembly is commanded off and the feedback voltage is lower than 2.45 volts.
^ The band control solenoid assembly is commanded off and the feedback voltage is 2.45-3.53 volts.
^ The band control solenoid assembly is commanded on and the feedback voltage is greater than 4.02 volts.

ACTION TAKEN WHEN THE DTC SETS
^ The TCM flashes the sport mode lamp and sends a MIL request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.
^ The ECM records the operating conditions in the Freeze Frame at the time of the MIL request from the TCM.
^ The transmission operates in the default mode (maximum line pressure, command 4th gear, inhibit TCC, freeze shift adapts).

CONDITIONS FOR CLEARING THE MIL/DTC
^ The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL request.
^ A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the MIL/DTC.
^ The TCM cancels the DTC default mode actions when the ignition switch is Off long enough in order to power down the TCM.

DIAGNOSTIC AIDS
Use the J 35616-A connector test adapter kit for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:
^ Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Refer to General Electrical Diagnosis Procedures in Diagrams for proper procedure.
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

TEST DESCRIPTION

Steps 1 - 10:

Steps 11 - 15:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the solenoid operates. Ground the circuit repeatedly if necessary.
7. If the TCC solenoid valve checks out OK and no condition is found with the connections at the TCM, check the wiring and connections closely. If no condition is found, the TCM may be the cause of the condition.