GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 Vibe - AWD 🢒 Restraints 🢒 SIR 🢒 DTC P2646

Circuit Description

The DTC P2646 Rocker Arm Actuator System Stuck Off diagnostic monitors the operation of the rocker arm oil control solenoid. The rocker arm oil control solenoid enables the powertrain control module (PCM) to operate the high speed cam system. The high speed cam system significantly increases valve lift at engine speeds above 6,000 RPM. A second camshaft lobe with a high lift profile is cast into each camshaft, alongside the low/medium speed lobes. Unique rocker arms follow both the high speed and low/medium speed cam lobes. At engine speeds below 6,000 RPM, the low/medium speed cam lobes operate the rocker arms. When the rocker arm oil control solenoid is turned ON between 6,000-8,200 RPM, the rocker arms are operated by the high speed cam lobes. The rocker arm oil control solenoid is controlled by a pulse width modulated (PWM) signal from the PCM.

The rocker arm oil pressure switch detects oil pressure when oil is flowing thorough the rocker arm oil supply system. When the rocker arm oil control solenoid is ON, the oil pressure switch opens and the signal circuit to the PCM goes high. A DTC P2646 sets when the signal circuit of the rocker arm oil pressure switch remains low even when engine speed is more than 6,000 RPM. For additional information on the operation of the rocker arm oil control system, refer to Rocker Arm Oil Control System Description .

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2646 Rocker Arm Actuator System Stuck Off

Conditions for Running the DTC
    • DTCs P0100, P0101, P0102, P0103, P0115, P0117, P0118, P0125, P0335, P0340, P0341, P0385 are not set.
    • The engine has been running at least 10 seconds.
    • Engine speed is more than 6,500 RPM.
    • The engine coolant temperature (ECT) is at least 60°C (140°F).
    • The vehicle is operating at more than 10 km/h (6 mph).
    • DTC P2646 runs continuously when the above conditions are met.

Conditions for Setting the DTC
    • The signal circuit of the rocker arm oil pressure switch stays low.
    • The above condition is present for at least 5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM stores the conditions that were present when the DTC set as Freeze Frame data.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
    • A DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear DTC Information function.

Test Description

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

  1. The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool, if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks the operation of the rocker arm oil control solenoid. When commanded ON, the rocker arm oil control solenoid increases valve lift enough to cause the engine to run rough or to stall.

    3.

  3. This step visually inspects the operation of the rocker arm oil control solenoid. The solenoid plunger and spool valve movement should be smooth and rapid from extended to retracted.

    4.

  4. This step tests the operation of the rocker arm oil pressure switch. The oil pressure switch is normally closed to ground with less than 20.7 kPa (3 psi) of oil pressure. With the oil control solenoid energized oil pressure will open the switch and the test lamp should turn Off momentarily before the engine stalls.

    5.

  5. This step checks for electrical resistance in the wiring and connections of the rocker arm oil control solenoid circuit. Circuit resistance as small as 25 ohms can cause the solenoid to malfunction and a DTC P2646 to set.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Disconnect the rocker arm oil control solenoid.
  2. Measure the resistance of the solenoid with a DMM.

Is the resistance within the specified range?

6.9-7.9 ohms at 20°C (68°F)

Go to Step 3

Go to Step 12

3

  1. Start the engine.
  2. Allow the engine to reach normal operating temperature.
  3. With the transmission in neutral, increase the engine speed to 1,500-2,500 RPM.
  4. Command the rocker arm oil control solenoid ON with a scan tool. Refer to Scan Tool Output Controls .

Does the engine idle very rough or stall when the rocker arm oil control solenoid is commanded ON?

--

Go to Step 7

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Remove the rocker arm oil control solenoid. Refer to Rocker Arm Oil Control Solenoid Valve Replacement .
  3. Connect the rocker arm oil control solenoid to B+ and ground with a pair of fused jumper wires.
  4. Observe the movement of the solenoid plunger when electrical voltage is applied and removed.

Does the solenoid plunger extend to the specified value when voltage is applied and then retract smoothly when voltage is removed?

3 mm (0.125 in)

Go to Step 5

Go to Step 11

5
  1. Remove the rocker arm oil control solenoid oil filter. Refer to Rocker Arm Oil Control Solenoid Valve Filter Replacement .
  2. Inspect the oil filter for restrictions or blockage.

Is the rocker arm oil control solenoid oil filter restricted or blocked?

--

Go to Step 10

Go to Step 6

6
  1. Inspect for the following conditions:
    2. • Blockage or restrictions in the oil passages of the rocker arm oil control solenoid housing
    • Blockage or restrictions in the cylinder head oil passages or rocker arm shafts
    • The correct operation of the rocker arm shafts and rocker arms
  2. Repair as necessary. Refer to Diagnostic Starting Point - Engine Mechanical in Engine Mechanical.

Did you complete the repair?

--

Go to Step 15

--

7
  1. Disconnect the electrical connector of the rocker arm oil pressure switch.
  2. Connect a DMM to the oil pressure switch electrical connector and ground.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the DC voltage.

Is the voltage more than the specified value?

11 V

Go to Step 8

Go to Step 9

8

  1. Connect a test lamp to B+ and the terminal of the oil pressure switch.
  2. Start the engine.
  3. The test lamp should be illuminated.
  4. With the transmission in neutral and the engine at normal operating temperature, increase the engine speed to 1,500-2,500 RPM.
  5. Observe the test lamp while commanding the rocker arm oil control solenoid ON with the scan tool.

Did the test lamp turn OFF when the rocker arm oil control solenoid was commanded ON?

--

Go to Intermittent Conditions

Go to Step 13

9
  1. Inspect for a short to ground in the input circuit of the rocker arm oil pressure switch.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 15

Go to Step 14

10
  1. Clean or replace the rocker arm oil control solenoid filter. Refer to Rocker Arm Oil Control Solenoid Valve Filter Replacement .
  2. Install the rocker arm oil control solenoid. Refer to Rocker Arm Oil Control Solenoid Valve Replacement .

Did you complete the replacement?

--

Go to Step 15

--

11

  1. Check the electrical circuit of the rocker arm oil control solenoid for high resistance in the circuit wiring or connections.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 15

Go to Step 12

12

Replace the rocker arm oil control solenoid valve. Refer to Rocker Arm Oil Control Solenoid Valve Replacement .

Did you complete the replacement?

--

Go to Step 15

--

13

Replace the rocker arm oil pressure switch. Refer to Rocker Arm Oil Pressure Switch Replacement .

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the powertrain control module (PCM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 16

Go to Step 2

16

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK