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 P0842 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0842 Transmission Pressure Switch 1 Circuit Low
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 OFF, destroked, position. |
Conditions for Setting the DTC
DTC P0842 sets during steady state operation when PS1 indicates ON for 125 milliseconds after shift solenoid 1 (SS1) has been commanded OFF.
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL). |
| • | When in a forward range, 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 while diagnostic response is active. |
| • | If 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. |
| • | If the shift selector is moved to REVERSE, the transmission will shift to REVERSE if it is not compromised by overspeeding or a direction change. If compromised, the transmission will shift to NEUTRAL. |
| • | DTC P0842 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. |
| • | This DTC may indicate that SS1 is mechanically defective or the shift valve is stuck in the stroked state. |
| • | When DTC P0752 and P0842 are set in combination, this may indicate a short to ground at the pressure switch circuit or the shift valve is stuck in the stroked state. |
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 | Yes | No |
|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
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 PS1 status is LOW? | Go to Diagnostic Aids | Go to Step 5 |
Does the scan tool indicate PS1 status is LOW when grounded and HIGH when open? | Go to Step 6 | Go to Step 12 | |
Does the scan tool indicate PS1 status is LOW when grounded and HIGH when open? | Go to Step 7 | Go to Step 11 | |
Does the scan tool indicate PS1 status is LOW when grounded and HIGH when open? | Go to Step 8 | Go to Step 10 | |
Does the scan tool indicate PS1 status is LOW when grounded and HIGH when open? | Go to Diagnostic Aids | Go to Step 9 | |
9 | Replace the PSM. Refer to Pressure Switch Manifold Replacement . Did you complete the replacement? | Go to Step 13 | -- |
10 | Replace the AT internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement? | Go to Step 13 | -- |
11 | Test the PS1 circuit between the TCM and AT inline 20-way connector for an open or short condition. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 13 | -- |
12 |
Important: Prior to replacing the TCM, swap the TCM with a known good TCM. In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | -- |
13 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | Go to Step 14 | Go to Step 2 |
14 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
