Circuit Description
Trim B solenoid is used to control on-coming, off-going, and holding pressure in any one of the five clutches. B solenoid is referred to as a pressure proportional to current (PPC) solenoid, since the output hydraulic pressure supplied by this solenoid is proportional to the controlled current command.
The transmission control module (TCM) uses information from the turbine and output speed sensors to detect if a clutch is slipping. The clutch being controlled by the B solenoid will vary, depending on the shift that was being completed.
DTC P1721 is a type A DTC.
Conditions for Running the DTC
| • | The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts. |
| • | Turbine speed is greater than 60 RPM. |
| • | Output speed is greater than 125 RPM. |
| • | The transmission is at normal operating temperature. |
Conditions for Setting the DTC
DTC P1721 sets when the TCM detects an incorrect on-coming ratio, during a forward range shift, for an accumulated number of occurrences.
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL). |
| • | When failure occurs in a forward range, the transmission will go to the previous range. If failure occurs in NEUTRAL or REVERSE, the transmission will lock in NEUTRAL while diagnostic response is active. |
| • | If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL, and in some cases may lock in NEUTRAL. |
| • | If the shift selector is moved to REVERSE, the transmission will shift to REVERSE or NEUTRAL. |
| • | If the shift selector is returned to a forward range and the transmission is compromised by overspeeding or direction change, the transmission will shift to NEUTRAL. |
| • | DTC P1721 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. Look 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 indicates that the on-coming clutch, being controlled by the B solenoid, is not applied or applied too slowly. This could indicate a leak or obstruction in a specific clutch apply circuit. Observe scan tool failure record data for previous or current range information when the DTC was set, in order to determine the specific shift when the DTC was set. Refer to Solenoid and Clutch Chart in order to determine which clutch circuit is suspect. |
| Important: Clutch failure due to installation of an engine power upgrade is not covered under the manufacturers warranty. |
| • | Inspect for the presence of an add-on engine power package. When engine horsepower or torque is increased over factory rating, a shift flare condition may occur. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for proper ignition voltage.
-
This step tests for erratic speed sensor readings.
-
This step tests for internal hydraulic leakage.
-
This step tests for clutch capacity.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Automatic Transmission? | -- | Go to Step 2 | |
2 | Check the transmission fluid level. Refer to Transmission Fluid Check . Is the transmission fluid level correct? | -- | Go to Step 3 | Go to Transmission Fluid Check |
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. Is voltage within the specified range? | 9-18 V | Go to Step 4 | Go to DTC P0562 for low voltage or DTC P0563 for high voltage | |
Is speed sensor data erratic? | -- | Go to the appropriate speed sensor DTC | Go to Step 5 | |
Was the line pressure low in a specific range or in ranges where the same clutch was applied? | -- | Go to Step 6 | ||
|
Notice: Refer to Transmission Stall Test Notice in the Preface section. Conduct a clutch test for all forward ranges. Refer to Clutch Test . Did turbine speed remain at zero in all ranges? | -- | Go to Diagnostic Aids | Go to Step 7 | |
7 |
Are there signs of clutch failure? | -- | Go to Step 8 | Go to Step 9 |
8 | Remove the transmission for overhaul or replacement. Refer to Transmission Replacement . Did you complete the repair or replacement? | -- | Go to Step 11 | -- |
9 | Inspect for a stuck or sticking B trim valve. Refer to Control Valve Body Cleaning and Inspection . Did you find and repair a condition? | -- | Go to Step 11 | Go to Step 10 |
10 | Replace B solenoid. Refer to Control Valve Solenoid Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
11 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK | Go to Step 1 |
