Technical Description of OBD-II Trouble Code
The circuit for controlling the exhaust valve solenoid is experiencing low voltage (Bank 2).
What does that mean?
This code is a generic OBD-II powertrain code that applies to all vehicle makes and models (1996-newer). However, the specific repair steps may vary depending on the model.
In vehicles equipped with variable valve timing (VVT), the Engine Control Module / Powertrain Control Module (ECM/PCM) regulates the camshaft position by controlling the engine oil flow through the control solenoid. The control solenoid is activated by a Pulse Width Modulated signal (PWM) from the ECM/PCM. The ECM/PCM monitors this signal and if the voltage is below the specified range, it will trigger this trouble code and illuminate the Malfunction Indicator Lamp (MIL).
Bank 2 refers to the side of the engine that does not contain cylinder #1 – make sure to verify this according to the manufacturer’s specifications. The exhaust valve control solenoid is typically located on the exhaust manifold side of the cylinder head. This code is similar to codes P0084 and P0086. It may also be accompanied by code P0029.
Symptoms
The symptoms may include:
Potential Causes
The potential causes of a P0085 diagnostic trouble code may include:
Diagnostic Steps
Wire harness – Disconnect the harness connectors from the PCM/ECM. Using a wiring diagram, locate the + and – wires connected to the solenoid. The solenoid can be either ground side or power side controlled, depending on the application. Refer to the factory wiring diagrams to determine the power flow in the circuit. Using a digital volt ohm meter (DVOM) set to the volts setting, check for voltage by placing the positive lead on the vehicle battery and the negative lead on each wire connected to the control solenoid. Depending on the application, if the solenoid is grounded to the chassis, test the power lead to the control solenoid at the PCM/ECM wiring harness – there should be no voltage present. If there is voltage present, check for a short to ground in the wiring up to the control solenoid by disconnecting connectors and working back to the solenoid.
Control solenoid – Check for a short to ground through the control solenoid by placing either DVOM lead on a known good ground and the other lead on each terminal of the control solenoid. If there is low resistance, the solenoid may be internally shorted.
PCM/ECM – If all wiring and the control solenoid check out okay, it will be necessary to monitor the solenoid during engine operation by back probing the wires at the PCM/ECM. Use an advanced scan tool that can read the engine functions to monitor the duty cycle commanded to the control solenoid. It will be necessary to monitor the solenoid under various engine RPMs and load. Use an oscilloscope or graphing multimeter set to the duty cycle scale, connect the negative lead to a known good ground and the positive lead to either wire terminal at the solenoid itself. The reading on the multimeter tool should match the commanded duty cycle on the scan tool. If they are opposite, the polarity may be reversed – connect the positive lead to the other wire terminal of the solenoid and re-test to verify. If no signal is detected from the PCM, there may be a fault with the PCM itself.
