P0085 — Exhaust Valve Control Solenoid

The Diagnostic Trouble Code (DTC) P0085 generally indicates a problem with the exhaust valve control solenoid circuit. This component plays a critical role in controlling the exhaust valve’s operation, often in vehicles equipped with variable valve timing (VVT) or exhaust system adjustments. If the ECU (Engine Control Unit) detects an issue with this solenoid, it will trigger this fault code to alert the driver or technician of a potential fault.

Note that labeling variations for this code may occur between vehicle manufacturers and different OEMs, but the underlying diagnostic concept remains similar.

—

Manufacturer variations for trouble code P0085

Different vehicle manufacturers may assign their own specific labels or code formats for issues related to the exhaust valve control solenoid. However, P0085 typically points to an electrical or mechanical fault within the related circuit. Below are some common manufacturer-specific labels or codes associated with similar issues:

• Volkswagen / Audi: 17664 / P0085 (related to exhaust valve control solenoid circuit)
• BMW: Specific codes may vary but relate to variable valve timing control circuits
• Ford: Similar codes may reference exhaust variable valve timing control circuit issues
• Others: Variations depend on OEM coding conventions, but diagnostic context remains consistent

—

What does trouble code P0085 mean?

P0085 indicates that the Engine Control Unit (ECU) has detected a problem within the exhaust valve control solenoid circuit. This solenoid is responsible for regulating the exhaust valves’ movement, often in tandem with variable valve timing (VVT) systems, to optimise engine efficiency and emissions.

The ECU monitors the entire circuit, including the solenoid’s electrical characteristics such as voltage, resistance, and response time. When it detects irregularities—be it a short circuit, open circuit, or malfunction—it will set this fault code.

This issue often arises in scenarios where the solenoid fails, wiring becomes damaged, or the control valve itself is faulty. It can also be triggered if there’s a problem with the related oil pressure or hydraulic system, but typically it points to an electrical circuit concern.

In simple terms: P0085 means that the vehicle’s brain has sensed something wrong with the system that controls the exhaust valve’s movement — either an electrical problem or a mechanical fault preventing proper operation.

—

Severity and risks of trouble code P0085

The P0085 code is classified as a moderate severity fault because it can impact engine performance, emissions, and fuel efficiency. If ignored, it may lead to increased emissions, decreased fuel economy, or potential long-term damage to the exhaust and variable valve timing components.

However, it is usually not an immediate threat to engine safety or drivability. Vehicles may experience some performance issues, but typically, you can operate the vehicle with caution. Nevertheless, it’s recommended to diagnose and repair this issue promptly to avoid further complications.

**Can the vehicle be driven?** Limited — you should avoid prolonged driving and seek diagnosis as soon as possible. Under certain conditions, such as severe circuit faults, driving may be possible but is not advisable for extended periods.

—

Symptoms of trouble code P0085

Owners or mechanics might notice several signs when this code is active, although it might not always trigger noticeable symptoms immediately. Common symptoms include:

• Engine warning light illuminated on the dashboard
• Reduced engine performance, especially at low or medium speeds
• Decreased fuel economy
• Rough idling or misfires
• Possible increase in exhaust emissions
• Unusual exhaust smell or noise in some cases
• Inconsistent or reduced torque delivery

It’s important to remember that these symptoms are not exclusive to P0085 and may overlap with other engine or control system issues. Proper diagnostics are essential to pinpoint the problem accurately.

—

Most likely causes of trouble code P0085

Diagnosing P0085 involves understanding common faults that trigger circuit irregularities. Some causes are more prevalent than others, and their identification can streamline repair efforts.

1. Faulty or failing exhaust valve control solenoid: The solenoid itself may be defective due to internal failure or wear over time.
2. Electrical wiring issue: Damaged, corroded, or disconnected wiring harnesses and connectors can interrupt circuit signals.
3. Poor electrical connection: Loose or corroded connectors leading to insufficient or inconsistent electrical flow.
4. Oil pressure or hydraulic problem: Since some systems rely on hydraulic pressure for operation, issues here can mimic electrical faults.
5. ECU or software malfunction: Rarely, the vehicle’s electronic control unit may misinterpret signals due to software glitches or internal faults.
6. Mechanical failure of the exhaust valve control mechanism: In cases where the physical valve or associated parts are obstructed or damaged, the circuit may register as faulty.

—

How to diagnose trouble code P0085

Diagnosing P0085 requires a systematic approach, combining visual inspections with live data analysis and electrical tests. Here are some generic steps you can follow:

1. Check for other related fault codes: Look for codes linked to VVT, exhaust system, or other control modules that may provide clues.
2. Visual inspection of wiring and connectors: Examine the harnesses, connectors, and ground points related to the exhaust valve control circuit for damage, corrosion, or disconnection.
3. Inspect the solenoid and associated components: Check for physical damage or signs of failure such as leaks, cracks, or corrosion.
4. Test electrical resistance and continuity: Use a multimeter to verify the wiring integrity and solenoid coil resistance as per manufacturer specifications.
5. Perform live data monitoring: Using a scan tool or diagnostic interface, observe the command signals and response of the exhaust valve control solenoid while the engine runs.
6. Check oil pressure and hydraulic systems: Since some variable valve systems rely on hydraulic elements, ensure oil pressure and fluid levels are within specifications.
7. Update or reflash ECU software: In rare cases, software issues may cause false readings; updating to the latest OEM firmware can resolve this.

—

Possible repairs for trouble code P0085

Repairs will depend on the identified root cause, but generally, the following actions could resolve the issue:

• Replace the exhaust valve control solenoid: If the coil or physical valve is defective, a professional replacement is typically required.
• Repair or replace damaged wiring and connectors: Restoring proper electrical connections involves repairing or replacing affected harness segments.
• Clean or replace related mechanical components: Mechanical issues such as obstructions or seized valves necessitate mechanical repairs or replacements.
• Address hydraulic system issues: Low oil pressure or contaminated fluid should be corrected, which may involve oil change or hydraulic system repair.
• Update ECU firmware: Ensuring the control software is current can eliminate software-related faults.

Note: Some repairs should be carried out by a qualified technician due to the complexity and need for precise electrical or mechanical work.

—

Vehicles commonly associated with trouble code P0085 in Europe

This fault code can occur in a variety of vehicles, especially those equipped with variable valve timing systems. While the exact prevalence varies, certain brands and engine families are known to be affected more often:

Volkswagen Group (Volkswagen, Audi, SEAT, Škoda): Many models with TSI, TFSI, or EA888 engines have reported similar issues related to exhaust valve control circuits.

BMW: Vehicles with BMW’s VANOS system, especially N20 and N55 engine families, may experience related faults.

Ford: Certain EcoBoost models might report issues linked to variable valve timing control circuits.

In general, vehicles with complex variable valve timing systems are more susceptible to P0085-related faults, primarily depending on their design and maintenance history.

—

Frequent mistakes with trouble code P0085

Diagnosis and repair of P0085 can be tricky. Common mistakes include:

• Ignoring minor electrical issues: Small wiring problems can escalate if not addressed early, leading to misleading diagnostics.
• Replacing parts without thorough testing: Changing the solenoid or wiring without proper electrical testing may result in unnecessary repairs.
• Overlooking other related systems: Failing to check oil pressure or hydraulic systems that affect the control circuit can lead to incomplete diagnostics.
• Misinterpretation of data: Relying solely on scanner readings without visual inspection or live data can lead to misdiagnosis.
• Ignoring software updates: Outdated ECU firmware can cause false fault codes or poor system responses.

—

FAQ — trouble code P0085

Can this code disappear on its own?

In some cases, minor electrical glitches or temporary circuit faults may cause the P0085 code to clear after a short drive or system reset. However, if the underlying issue persists, the code will likely return.

Can I keep driving?

While the vehicle may be drivable with P0085 active, it is advised to limit driving and seek professional diagnosis. Ignoring the fault can lead to further damage or emissions issues, and in some cases, the vehicle may enter a limp mode to protect itself.

Why does the code return after clearing?

The fault may be caused by intermittent electrical connections, failing components, or unresolved mechanical issues. If these are not correctly addressed, the code will reappear after reset.