DTC P0751 1-2 Shift Solenoid Valve Performance. Cadillac DeVille 1998

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The Powertrain Control Module (PCM) identifies a 1-2 shift solenoid valve problem by monitoring the commanded gear ratio versus the actual gear ratio.

If the PCM detects a gear ratio that is outside the limits for a particular commanded gear, then DTC P0751 sets. DTC P0751 is a Type A DTC.

Conditions for Setting the DTC

•	No MAF DTCs P0101, P0102 or P0103.

•	No TP DTCs P0121, P0122 or P0123.

•	No VSS DTCs P0502 or P0503.

•	No A/T ISS DTCs P0716 or P0717.

•	No 1-2 shift solenoid valve electrical DTC P0753.

•	No 2-3 shift solenoid valve electrical DTC P0758.

•	No TFP Val. Position Sw. DTC P1810.

•	No TCC PWM Solenoid valve DTC P1860.

•	The engine run time is greater than 5 seconds.

•	The engine is not in fuel cut off.

•	The TFP Val. Position Sw. indicates D1, D2, D3 or D4.

•	The vehicle speed is greater than 6 km/h (4 mph).

•	A shift is not in progress.

•	The throttle angle is greater than 11 degrees.

•	The transmission fluid temperature is greater than -18°C (0°F).

Failure Criteria

Case 1

•	First gear is commanded.

•	The gear ratio is 1.54-1.71 for 1 second.

•	Delivered torque is greater than 82 N·m (60 lb ft).

Case 2

•	Second gear is commanded.

•	The gear ratio is 2.87-3.11 for 3 seconds.

•	Delivered torque is greater than 96 N·m (70 lb ft).

Case 3

•	Third gear is commanded.

•	The gear ratio is 0.65-0.71 for 3 seconds.

•	Delivered torque is greater than 82 N·m (60 lb ft).

Case 4

•	Fourth gear is commanded.

•	The gear ratio is 0.95-1.05 for 5 seconds.

•	Delivered torque is greater than 96 N·m (70 lb ft).

Action Taken When the DTC Sets

•	The PCM illuminates the Malfunction Indicator Lamp (MIL).

•	SERVICE ENGINE SOON, SERVICE TRANSMISSION displays on the Driver Information Center (DIC).

•	The PCM commands 2nd gear.

•	The PCM commands default line pressure

•	The PCM inhibits TCC engagement.

•	The PCM disables steady state adapts

•	The PCM disables garage shift adapts

•	DTC P0751 is stored in the PCM history.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL after three consecutive trips without a failure reported.

•	A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

•	The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids

•	Inspect the transmission fluid for sediment.

•	Inspect the transmission filter for debris.

•	Refer to the Shift Solenoid Valve State and Gear Ratio table.

Test Description

Important: Do not drive the vehicle for an extended period of time, because additional internal damage may occur.

The numbers below refer to the step numbers on the diagnostic table.

This step verifies that DTC P0751 is set. Set up data pairs (current gear and gear ratio) on the Scan Tool . Drive the vehicle while commanding First gear with the Scan Tool .

This step verifies that the gear ratio indicated a Second gear start, and the vehicle does not achieve First gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates Third gear and the vehicle does not achieve Fourth gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates First gear and the vehicle does not achieve Second gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates Fourth gear and the vehicle does not achieve Third gear. The list of components should be inspected and repaired if faulty.

DTC P0751 1-2 Shift Solenoid Valve Performance

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls

Have you performed the transmission fluid checking procedure?

Go to Step 3

Go to Transmission Fluid Check

Install the Scan Tool .
With the engine OFF, turn the ignition switch to the RUN position.

Important: Before clearing the DTC(s), use the Scan Tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM.

Record the DTC Freeze Frame and Failure Records, then clear the DTC(s).
Using the Scan Tool , enter the Shift Transmission function.
Monitor the Current Gear and Gear Ratio data pairs:
Accelerate the vehicle and command First gear.

Is the gear ratio within the specified parameters?

1.54-1.71

Go to Step 4

Go to Step 5

Inspect the following items:

•	A damaged Lo/Rev servo apply pin

•	The 1-2 shift valve is stuck in upshifted position, or the valve contains debris

•	The FWD/CC support seals are damaged

•	The FWD/CC studs are damaged or broken

•	The Lo roller clutch is worn or damaged

•	The forward clutch piston is damaged or cracked

•	The forward clutch piston seals are rolled, cut or damaged

•	The support housing seal rings are leaking, damaged or cut

•	The forward sprag is damaged or not holding

•	The check ball is missing or stuck

Repair or replace any of the items if necessary.

Refer to Transmission Overhaul in the 4T80-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

Accelerate the vehicle and command a 3-4 shift.

Is the gear ratio within the specified parameters?

0.95-1.05

Go to Step 6

Go to Step 7

Inspect the following items:

•	The 1-2 shift solenoid valve for debris

•	The fourth band is burned or slipping

•	The fourth servo pin is broken or seized

•	The fourth servo piston is damaged

•	The fourth servo seals are rolled, cut or damaged

•	The fourth servo cover is cracked

•	The 3-4 shift valve bore plug is misassembled

Repair or replace any of the items if necessary.

Refer to Transmission Overhaul in the 4T80-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

Accelerate the vehicle and command a 1-2 shift.

Is the gear ratio within the specified parameters?

2.87-3.11

Go to Step 8

Go to Step 9

Inspect the following items:

•	The 1-2 shift solenoid valve for debris

•	The 1-2 shift valve is stuck in 1st gear

•	The clutch plates are burned or damaged

•	The piston assembly in 2nd clutch is cracked or damaged

•	The 2nd clutch return spring is broken or out of position

•	The piston seals on the piston/2nd clutch are rolled, damaged or leaking

•	The 2nd sprag is not holding or is damaged

Repair or replace any of the items if necessary.

Refer to Transmission Overhaul in the 4T80-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

Accelerate the vehicle and command a 2-3 shift.

Is the gear ratio within the specified parameters?

0.65-0.71

Go to Step 10

Go to Diagnostic Aids

Inspect the following items:

•	The 1-2 shift solenoid valve for debris

•	The exhaust valve cup plug for the driven sprocket support or valve improperly installed.

•	The third clutch plates are burned or contain damaged splines

•	The third clutch piston is cracked or damaged, or the piston contains check ball damage

•	The third clutch seals on piston are rolled, damaged or leaking

•	The check ball is missing or stuck

Repair or replace any of the items if necessary.

Refer to Transmission Overhaul in the 4T80-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

In order to verify your repair, perform the following procedure:

Select DTC.
Select Clear Info.
Operate the vehicle under the following conditions:

•	Road test the vehicle with the gear select lever in D4.

•	Ensure all four gears are achieved.

Select Specific DTC.
Enter DTC P0751.

Has the test run and passed?

System OK

Go to Step 1