P0079 B1 Exhaust Valve Control Solenoid Circuit Low
Content
P0079 B1 Exhaust Valve Control Solenoid Circuit Low
OBD-II DTC Datasheet
Low signal level in the solenoid valve circuit of the exhaust valve control (Bank 1)
What does this mean?
This code is a generic OBD-II powertrain code, which means it applies to all makes and models of vehicles (1996 and newer), although specific repair steps may differ depending on the model.
On vehicles equipped with a variable valve timing (VVT) system, the engine control module / powertrain control module (ECM / PCM) monitors the camshaft position by adjusting the engine oil level with the camshaft position control solenoid. The control solenoid is controlled by a pulse width modulated (PWM) signal from the ECM / PCM. The ECM / PCM monitors this signal and, if the voltage is below specification, it sets this DTC and illuminates the Malfunction Indicator Lamp (MIL).
Bank 1 refers to the #1 cylinder side of the engine - be sure to check according to the manufacturer's specifications. The exhaust valve control solenoid is usually located on the exhaust manifold side of the cylinder head. This code is similar to codes P0078 and P0080. This code may also be accompanied by P0027.
symptoms
Symptoms may include:
- Malfunction Indicator Lamp (MIL) illuminated
- Poor acceleration
- Reduced fuel economy
Possible reasons
Possible causes of DTC P0079 may include:
- The wiring harness is shorted to ground
- Electromagnetic short to ground
- Defective ECM
Diagnostic steps
Wiring Harness - Disconnect the harness connectors from the PCM/ECM using the wiring diagram, locate the + and - wires to the solenoid. The solenoid can be driven from the ground side or from the power side, depending on the application. Refer to the factory wiring diagrams to determine the power flow in the circuit. Using a digital voltmeter (DVOM) set to the volts setting, check the voltage on the positive vehicle battery wire and the negative wire on each wire to the control solenoid. Depending on the application, if the solenoid is grounded to the chassis, check the power wire to the control solenoid in the PCM/ECM wiring harness, there should be no voltage present. If voltage is present, check for a short to ground in the wiring to the control solenoid by disconnecting the connectors and returning to the solenoid.
Control Solenoid - Check for a short to ground through the control solenoid by connecting one lead of the DVOM to a known good ground and the other to each terminal on the control solenoid. If the resistance is low, the solenoid may be shorted internally.
PCM/ECM - If all wiring and control solenoid are OK, it will be necessary to monitor the solenoid while the engine is running by checking the wires to the PCM/ECM. Using an advanced scan tool that reads engine functions, monitor the duty cycle set by the control solenoid. It will be necessary to control the solenoid while the engine is running at various engine speeds and loads. Using an oscilloscope or graphical multimeter set to duty cycle, connect the negative wire to a known good ground and the positive wire to any wire terminal on the solenoid itself. The multimeter reading should match the specified duty cycle on the scan tool. If they are opposite, the polarity may be reversed - connect the positive wire on the other end of the wire to the solenoid and repeat the test to check. If no signal is found from the PCM, the PCM itself may be faulty.
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