Circuit Description
The pressure switch manifold (PSM) is a multiple-switch assembly made up of three normally open (N/O) and one normally closed (N/C) pressure switches. The C pressure switch monitors C shift valve positioning and relays it to the transmission control module (TCM). When C pressure switch is in the open state, C shift valve should be in the unstroked position.
DTC P0843 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0843 Pressure Switch C 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. |
| • | C shift valve is commanded to the ON, stroked, position. |
Conditions for Setting the DTC
DTC P0843 sets during steady state operation when C solenoid is commanded ON and C pressure switch 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 over speeding 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 will be 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. |
| • | This DTC may indicate C solenoid is mechanically defective. |
| • | When a P0843 and P0841 are set in combination, this may indicate an open circuit condition is present at the pressure switch circuit or the shift valve is stuck in the unstroked position. |
| • | This DTC can be caused by a loss of prime. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the TCM response function.
-
This step tests the transmission wiring harness integrity.
-
This step tests and evaluates the internal wiring harness.
-
This step tests the PSM for a failed condition.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Measure the transmission fluid level. Refer to Transmission Fluid Check . Is the transmission fluid level correct? | -- | Go to Step 3 | Go to Transmission Fluid Check |
3 | Measure line pressure. Refer to Line Pressure Check . Is the pressure within the specified value? | -- | Go to Step 4 | |
4 |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Does the scan tool indicate TFP SW. C status is ON? | -- | Go to Diagnostic Aids | Go to Step 5 |
Does the scan tool indicate TFP SW. C status is ON when grounded and OFF when open? | -- | Go to Step 6 | Go to Step 15 | |
Does the scan tool indicate TFP SW. C status is ON when grounded and OFF when open? | -- | Go to Step 7 | Go to Step 14 | |
Does the scan tool indicate TFP SW. C status is ON when grounded and OFF when open? | -- | Go to Step 8 | Go to Step 13 | |
Does the scan tool indicate TFP SW. C status is ON when grounded and OFF when open? | -- | Go to Step 9 | Go to Step 12 | |
9 | Remove the control valve body and inspect for a stuck or sticking C shift valve. Refer to Control Valve Body Disassemble . Was the C shift valve stuck or sticking? | -- | Go to Step 11 | Go to Step 10 |
10 | Replace the C shift solenoid and install the control valve body. Refer to Control Valve Body Replacement . Did you complete the replacement of the solenoid and install the control valve body? | -- | Go to Step 16 | -- |
11 | Clean and inspect the related valves, bores, and the valve body for debris or contamination. Refer to Control Valve Body Cleaning and Inspection . Did you complete the replacement? | -- | Go to Step 16 | -- |
12 | Replace the PSM. Refer to Pressure Switch Manifold Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
13 | Replace the AT internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
14 | Repair the engine wiring harness circuit for an open or short. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
15 |
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | -- |
16 | Perform the following procedure in order to verify the repair:
Has test run and passed? | -- | System OK | Go to Step 1 |
