P0843
DTC P0843
Circuit Description
The pressure switch manifold (PSM) is a multiple-switch assembly made up of 3 normally open (N/O) pressure switches and 1 normally closed (N/C) pressure switch. Pressure switch 1 (PS1) monitors shift valve 1 positioning and relays it to the transmission control module (TCM).
DTC P0843 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0843 Transmission Pressure Switch 1 Circuit High
Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
^ Shift valve 1 is commanded to the ON, stroked, position.
Conditions for Setting the DTC
DTC P0843 sets during steady state operation when shift solenoid 1 (SS1) is commanded ON and PS1 indicates OFF for 0.1 second.
Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL).
^ When in a forward range and shifting is completed, the transmission will fail to another forward range, unless the transmission is compromised by overspeeding or direction change, then the transmission will shift to NEUTRAL.
^ When in a forward range and the shift is in process, the transmission will return to a previous range, except for 1-2 shifts and 2-1 shifts which will be completed.
^ When in NEUTRAL or REVERSE, the transmission will fail to NEUTRAL.
^ While diagnostic response is active, the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, then the transmission will shift to NEUTRAL.
^ DTC P0843 is stored in TCM history.
^ The TCM freezes shift adapts.
^ The TCM inhibits torque converter clutch (TCC) engagement.
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 Warm-up cycles without failure.
Diagnostic Aids
^ Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
^ A bent terminal
^ A backed-out terminal
^ A damaged terminal
^ Poor terminal tension
^ A chafed wire
^ A broken wire inside the insulation
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a condition.
^ When DTC P0751 and P0843 are set in combination, this may indicate an open circuit condition is present at the pressure switch circuit or the shift valve 1 is stuck in the destroked position.
^ This DTC may indicate that SS1 is mechanically defective.
^ This DTC can be caused by a loss of prime.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
5. This step tests the TCM response function.
6. This step tests the transmission wiring harness integrity.
7. This step tests and evaluates the internal wiring harness.
8. This step tests the PSM for a failed condition.
