GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Transmission/Transaxle 🢒 Automatic Transmission - ZF 4HP 16 🢒 DTC P1850

Circuit Description

The shift solenoids are 2 identical, normally open electronic exhaust valves that control upshifts and downshifts in all forward gear ranges. These shift solenoids work together in a combination of ON and OFF sequences to control the line pressure and shift mechanisms, such as clutches and brakes.

Solenoid 1 controls the high or low of the line pressure, the flow to each clutch valve, by the operation type ON/OFF. For example, solenoid 1 is ON, line pressure will be low, 599-799 kPa (87-116 psi) (6-8 bar). Solenoid 1 is OFF, line pressure will be high, 1 599-1 799 kPa, (232-261 psi) (16-18 bar). Solenoid 2 controls the oil flow to clutch valve E or lock-up clutch valve by the ON/OFF signal.

The transmission control module (TCM) monitors numerous inputs to determine the appropriate solenoid state combination and transaxle gear tor the vehicle operating conditions.

Conditions for Setting the DTC
    • Solenoid wiring shorted to ground
    • No DTC P1851, P1852.
    • Immediately after the above condition occurs

Action Taken When the DTC Sets
    • The hold lamp will blink.
    • The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.
    • Adopt Emergency/Substitute mode and constant 4th gear by hydraulic control.
    • After ignition OFF/ON: 3rd gear by hydraulic control. Possible P, R, and N also possible.

Conditions for Clearing the Hold Lamp/DTC
    • The hold lamp will turn OFF when the malfunction has not occurred after 3 ignition cycles.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Using a scan tool can clear history DTCs.

Diagnostic Aids

When DTC P1850 sets, the possible cause of the fault could be solenoid 1.

Step

Action

Values

Yes

No

1

Perform the Diagnostic System Check.

Is the check complete?

--

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Install the scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Record then clear the DTCs.
  4. Select Actuating on the scan tool.
  5. Actuate solenoid 1 ON/OFF.

Does the solenoid 1 change ON/OFF?

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the transaxle wiring connector.
  3. Measure the resistance between terminals 3 and 12 of the transaxle wiring connector.

Is the resistance within the specified value?

TFT 25°C (77°F)

26-34.5 ohms

Go to Step 7

Go to Step 4

4
  1. Remove the oil pan.
  2. Disconnect the wiring connector of solenoid 1.
  3. Measure the resistance between terminal 2 of solenoid 1 and ground.
  4. Measure the resistance between terminal 1 of solenoid 1 and ground.

Is the resistance at the specified value?

∞

Go to Step 6

Go to Step 5

5

Repair the internal line solenoid 1 for a short to ground.

Is the repair complete?

--

System OK

--

6

Replace solenoid 1.

Is the replacement complete?

--

System OK

--

7
  1. Disconnect the transaxle wiring connector and the transmission control module (TCM) connector.
  2. Measure the resistance between terminal 3 of the transaxle wiring connector and ground.
  3. Measure the resistance between terminal 12 of the transaxle wiring connector and ground.

Is the resistance at the specified value?

∞

Go to Step 9

Go to Step 8

8

Repair the transaxle wiring harness for a short to ground.

Is the repair complete?

--

System OK

--

9

Replace the TCM. Refer to Transmission Control Module Replacement .

Is the replacement complete?

--

Go to Step 10

--

10
  1. After the repair, use a scan tool Clear Info function.
  2. Road test the vehicle.
  3. Review the DTC info.

Has the last test failed or is the current DTC displayed?

--

Go to Step 2

System OK