1-2 and 2-3 Shift Solenoid Valves

1-2 and 2-3 Shift Solenoid Valves

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PATH: Diagnostics > Diagnostic Routines > Powertrain > Automatic Transmission - 4L60-E > Electronic Component Description

Electronic Component Description

• Astro, Safari (VIN M/L)
• Blazer - RHD (VIN S/T)
• Blazer, Bravada, Envoy, Jimmy, S10 Pickup, Sonoma (VIN S/T)
• Blazer, Bravada, Jimmy, S10 Pickup, Sonoma (VIN S/T)
• Camaro, Firebird (VIN F)
• Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
• Escalade, Pickup (Classic), Suburban, Tahoe, Yukon (VIN C/K)
• Express, Savana (VIN G)
• Isuzu (VIN S/T)
• S/T Isuzu (VIN S/T)
• Sierra, Silverado (VIN C/K)

Electronic Component Description

1-2 and 2-3 Shift Solenoid Valves

The 1-2 and 2-3 shift solenoid valves (also called A and B solenoids) are identical devices that control the movement of the 1-2 and 2-3 shift valves (the 3-4 shift valve is not directly controlled by a shift solenoid). The solenoids are normally open exhaust valves that work in four combinations to shift the transmission into different gears.

The PCM energizes each solenoid by grounding the solenoid through an internal quad driver. This sends current through the coil winding in the solenoid and moves the internal plunger out of the exhaust position. When ON, the solenoid redirects fluid to move a shift valve.

The PCM-controlled shift solenoids eliminate the need for TV and governor pressures to control shift valve operation.

3-2 Shift Solenoid Valve Assembly

The 3-2 shift solenoid valve assembly is an ON/OFF solenoid that is used in order to improve the 3-2 downshift. The solenoid regulates the release of the 3-4 clutch and the 2-4 band apply.

If a voltage fault is detected in the 3-2 shift solenoid circuit, diagnostic trouble code P0785 will set.

Transmission Pressure Control Solenoid

The transmission pressure control solenoid is an electronic pressure regulator that controls pressure based on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve.

The PCM controls the pressure control solenoid by commanding current between 0.1 and 1.1 amps. This changes the duty cycle of the solenoid, which can range between 5 percent and 95 percent (typically less than 60 percent). 1.1 amps corresponds to minimum line pressure, and 0.1 amps corresponds to maximum line pressure (if the solenoid loses power, the transmission defaults to maximum line pressure).

The PCM commands the line pressure values, using inputs such as the throttle position sensor.

The pressure control solenoid takes the place of the throttle valve or the vacuum modulator that was used on the past model transmissions.

If the duty cycle drops below 5 percent or rises above 95 percent, DTC P0748 will set.

Torque Converter Clutch Solenoid Valve

If a fault is detected in the TCC solenoid circuit, code P0740 will set.

The torque converter clutch solenoid valve is a normally open exhaust valve that is used to control torque converter clutch apply and release. When grounded (energized) by the PCM, the TCC solenoid valve stops converter signal oil from exhausting. This causes converter signal oil pressure to increase and shifts the TCC solenoid valve into the apply position.

The brake switch is an input to the PCM, and the PCM directly controls the TCC apply based on the brake switch status.

Torque Converter Clutch PWM Solenoid Valve

The torque converter clutch PWM solenoid valve controls the fluid acting on the converter clutch valve, which then controls the TCC apply and release. This solenoid is attached to the control valve body assembly within the transmission. The TCC PWM solenoid valve provides smooth engagement of the torque converter clutch by operating on a negative duty cycle a variable percent of ON time.

If a fault is detected in the TCC PWM circuit, code P1860 will set.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch

The transmission fluid pressure (TFP) manual valve position switch is a set of five pressure switches on the control valve body that sense whether fluid pressure is present in five different valve body passages. The combination of which switches are open and closed is used by the PCM in order to determine actual manual valve position. The TFP manual valve position switch, however, cannot distinguish between PARK and NEUTRAL because the monitored valve body pressures are identical in both cases.

The switches are wired to provide three signal lines that are monitored by the PCM. These inputs are used to help control line pressure, torque converter clutch apply and shift solenoid valve operation. Voltage at each of the signal lines is either zero or twelve volts.

In order to monitor the TFP manual valve position switch operation, the PCM compares the actual voltage combination of the switches to a TFP combination table stored in its memory. If the PCM sees one of two illegal voltage combinations, a DTC P1810 will result. A DTC P1810 indicates a short circuit condition in either the range signal A or the range signal C circuits.

The TFP manual valve position switch signal voltage can be measured from each pin-to-ground and compared to the combination table. On the automatic transmission (A/T) wiring harness assembly, pin N is range signal A, pin R is range signal B, and pin P is range signal C. With the A/T wiring harness assembly connected and the engine running, a voltage measurement of these three lines will indicate a high reading (near 12 volts) when a circuit is open, and a low reading (zero volts) when the circuit is switched to ground.

The transmission fluid temperature (TFT) sensor is part of the TFP manual valve position switch assembly.

Vehicle Speed Sensor

The vehicle speed sensor (or transmission output speed sensor) controls shift points and calculates the TCC slip.

The speed sensor contains a coil that gives off a continuous magnetic field. A rotor rotates past the sensor and the rotor teeth break the magnetic field. Each break in the field sends a pulse to the VSSB (Vehicle Speed Sensor Buffer). The VSSB sends two signals to the PCM. The first is a 2002 pulse per mile (PPM) signal that is used by the engine. The second is the transmission/transfer case 40 pulse per revolution (PPR) signal that is used in order to control the transmission.

In two wheel drive (2WD) applications, the vehicle speed sensor is located on the transmission extension housing. Trans Output Speed = Transfer Case Speed.

DTC P0502 will set if a fault exists in the vehicle speed sensor circuit 40 PPR line.

Automatic Transmission Fluid Temperature Sensor

The automatic transmission fluid temperature (TFT) sensor is part of the automatic transmission fluid pressure (TFP) manual valve position switch assembly. This sensor helps control torque converter clutch apply and shift quality.

The TFT sensor is a resistor, or thermistor, which changes value based on temperature. At low temperatures the resistance is high, and at high temperatures the resistance is low.

The PCM sends a 5 volt signal to the TFT sensor and the PCM measures the voltage drop in the circuit. You will measure a high voltage when the transmission is cold and a low voltage when the transmission is hot. Refer to the Temperature vs Resistance table.

If the TFT sensor circuit has a fault, DTC P0712 or P0713 is set. A DTC P0712 indicates a short circuit condition, while a DTC P0713 indicates an open circuit condition. DTC P0218 is set if the transmission is operating at a high temperature for a period of time.

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PATH: Diagnostics > Diagnostic Routines > Powertrain > Automatic Transmission - 4L60-E > DTC P0758 2-3 Shift Solenoid Circuit Electrical (4.3L)

DTC P0758 2-3 Shift Solenoid Circuit Electrical (4.3L)

• Blazer, Bravada, Envoy, Jimmy, S10 Pickup, Sonoma (VIN S/T)

DTC P0758 2-3 Shift Solenoid Circuit Electrical (4.3L)

Circuit Description

The 2-3 shift solenoid (SS) valve controls the fluid flow acting on the 2-3 shift valves. The solenoid is a normally-open exhaust valve. With the 1-2 SS valve, the 2-3 SS valve allows four different shifting combinations. The solenoid attaches to the control valve body within the transmission. The 2-3 SS valve receives ignition voltage through circuit 1020. The vehicle control module (VCM) controls the solenoid by providing the ground path on circuit 1223.

When the VCM detects a continuous open or short to ground in the 2-3 SS valve circuit or the 2-3 SS valve, then DTC P0758 sets. DTC P0758 is a type A DTC.

Conditions for Running the DTC

• The system voltage is 10-19 volts.
• The engine speed is greater than 450 RPM for 5 seconds.
• The engine is not in fuel cutoff.

Conditions for Setting the DTC

DTC P0758 sets if either of the following conditions occurs for 5 seconds:

• The VCM commands the solenoid ON and the voltage input remains high (B+).
• The VCM commands the solenoid OFF and the voltage input remains low (0 volts).

Action Taken When the DTC Sets

• The VCM illuminates the malfunction indicator lamp (MIL).
• The VCM commands third gear only.
• The VCM commands maximum line pressure.
• The VCM inhibits TCC engagement.
• The VCM freezes shift adapts from being updated.
• The VCM stores DTC P0758 in VCM history.

Conditions for Clearing the MIL/DTC

• The VCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
• A scan tool clears the DTC from VCM history.
• The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
• The VCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the VCM.

Diagnostic Aids

• Inspect the wiring at the VCM, the transmission connector and all other circuit connecting points for the following conditions:
• A backed out terminal
• A damaged terminal
• Reduced terminal tension
• A chafed wire
• A broken wire inside the insulation
• Moisture intrusion
• Corrosion

• When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.
• Refer to the Shift Solenoid Valve State and Gear Ratio table.
• A faulty ignition switch may set this code.

Test Description

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

1. This step tests the function of the 2-3 SS valve and the automatic transmission (A/T) wiring harness assembly.

1. This step tests for power to the 2-3 SS valve from the ignition through the fuse.

1. This step tests the ability of the VCM and of the wiring to control the ground circuit.

1. This step measures the resistance of the A/T wiring harness assembly and of the 2-3 SS valve.

DTC P0758 2-3 SS Circuit Electrical (4.3L)

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

1. Record the DTC Freeze Frame and Failure Records.
2. Clear the DTC.

• P0740
• P0753
• P0785
• P1860

1. Inspect the CLSTR fuse.
2. If the fuse is open, inspect the following components for a short to ground condition:
3. Circuit 1020 (PNK)
4. The solenoids
5. The A/T wiring harness assembly
6. Refer to General Electrical Diagnosis in Wiring Systems.

1. Repair the circuit, the solenoids and the harness if necessary.

1. Turn the ignition OFF.
2. Disconnect the transmission 20-way connector (additional DTCs may set).
3. Install the J 39775 jumper harness on the engine side of the 20-way connector.
4. With the engine OFF, turn the ignition switch to the RUN position.
5. Connect a test lamp from J 39775 jumper harness cavity E to ground.

1. Install a test lamp between cavity E and cavity B of the J 39775 jumper harness.
2. Using the transmission output control function on the scan tool, command the 2-3 SS valve ON and OFF three times.

1. Inspect circuit 1223 (YEL/BLK) of the engine wiring harness for an open, short to ground or short to power condition.

1. Repair the circuit if necessary.

1. Install the J 39775 jumper harness on the transmission side of the 20-way connector.
2. With the J 39200 DMM and J 35616-A connector test adapter kit, measure the resistance between terminal B and terminal E.

1. Disconnect the A/T wiring harness assembly from the 2-3 SS valve.
2. Measure the resistance of the 2-3 SS valve.

1. Disconnect the A/T wiring harness assembly from the 2-3 SS valve.
2. Measure the resistance from the component's terminals to ground.

1. Select DTC.
2. Select Clear Info.
3. Drive the vehicle in D4 and ensure the following conditions are met:
4. The VCM commands the 2-3 SS valve ON and the voltage input drops to zero.
5. The VCM commands the 2-3 SS valve OFF and the voltage input increases to B+.
6. All conditions are met for 5 seconds.

1. Select Specific DTC.
2. Enter DTC P0758.

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PATH: Diagnostics > Diagnostic Routines > Powertrain > Automatic Transmission - 4L60-E > DTC P0756 2-3 Shift Solenoid Valve Performance (2.2L)