P0033 – Turbocharger Bypass Valve Control Circuit/Open: Complete Mers Diagnostic Guide
Quick Summary: P0033 is an OBD-II trouble code indicating an electrical problem in the turbocharger bypass valve control circuit. This guide provides detailed diagnostics, repair procedures, and cost estimates specific to Mers vehicles.
P001 Code Definition and Technical Background
The P0033 diagnostic trouble code (DTC) indicates that your Mers’ Powertrain Control Module (PCM) has detected an abnormal electrical condition in the turbocharger bypass valve control circuit, specifically an “open” circuit condition.
P001.1 Turbocharger Bypass Valve Function
The turbocharger bypass valve (also called wastegate or blow-off valve) regulates boost pressure by diverting excess exhaust gases away from the turbine wheel. The control circuit consists of:
- Boost Control Solenoid – Electronic actuator controlled by the PCM
- Wiring Harness – Electrical connections between components
- PCM Control Signals – Pulse-width modulated signals from the engine computer
- Vacuum/Pressure Lines – Pneumatic connections in wastegate systems
- Wastegate Actuator – Mechanical component that moves the wastegate flap
P001.2 “Open Circuit” Condition Explained
An “open circuit” means the PCM detects infinite resistance in the control circuit when it expects a complete circuit with specific resistance values (typically 10-20Ω). This could be caused by:
- Broken or disconnected wiring in the control circuit
- Failed solenoid coil with internal break
- Corroded or damaged electrical connectors
- Blown fuse in the turbo control circuit
- Poor ground connection for the solenoid
- Internal PCM driver circuit failure (rare, <2% of cases)
Technical Note: Mers vehicles use a pulse-width modulated (PWM) signal to control the boost solenoid. The PCM monitors the circuit for expected current flow. An open circuit prevents current flow, triggering P0033.
P002 Symptoms and Immediate Effects
When P0033 appears, drivers typically experience one or more of these symptoms as the PCM implements failsafe strategies:
| Symptom Code | Symptom Description | Frequency | Severity | System Impact |
|---|---|---|---|---|
| S-001 | Illuminated Check Engine Light | 100% | Medium | Visual warning only |
| S-002 | Reduced engine power (Limp Mode) | 85% | High | Performance and safety impact |
| S-003 | Poor acceleration and turbo lag | 80% | Medium | Drivability concern |
| S-004 | Decreased fuel economy (10-15%) | 70% | Low | Economic impact |
| S-005 | Unusual turbo noises (whistling, whooshing) | 45% | Medium | Potential mechanical issue |
| S-006 | Boost pressure fluctuations | 60% | High | Potential engine damage |
Driving Safety Alert: While not immediately dangerous, continued driving with P0033 can lead to more serious turbocharger damage. We recommend addressing this issue promptly to avoid potential turbo replacement costs of $1,500-$4,000.
P003 Diagnostic Procedures and Testing
P003.1 Required Tools
P003.2 Step-by-Step Diagnostic Procedure
- 1Initial Code Verification: Use your OBD-II scanner to confirm P0033 is present and check for any additional codes that might indicate related issues.
- 2Visual Inspection (Code VIS-01):
- Locate the turbocharger bypass valve solenoid (typically mounted on or near the turbocharger assembly)
- Inspect wiring harness for chafing, burns, or damage, especially near hot components
- Check electrical connector for corrosion, bent pins, or improper seating
- Inspect vacuum lines (if applicable) for cracks, leaks, or disconnections
- Look for oil contamination around the solenoid, indicating turbo seal issues
- 3Fuse Check (Code FCHK-01): Locate and inspect the turbo system fuse (typically 10A-15A, check owner’s manual for exact location) in the engine bay fuse box.
- 4Solenoid Resistance Test (Code TEST-01):
// Test Procedure:
1. Disconnect electrical connector from solenoid
2. Set multimeter to resistance (Ω) mode
3. Measure resistance between solenoid terminals
4. Expected reading: 10-20 Ω for most Mers models
5. Reading of O.L or infinite resistance indicates faulty solenoid
6. Reading of 0Ω indicates shorted solenoid (different code) - 5Circuit Voltage Test (Code TEST-02):
// Test Procedure:
1. Reconnect electrical connector to solenoid
2. Set multimeter to DC voltage mode (20V range)
3. Back-probe connector with engine running
4. Check for PWM signal from PCM (varies with engine load)
5. Consistent 12V or 0V indicates circuit problem
6. Check for battery voltage at one terminal with key ON - 6Wastegate Actuator Test (Code TEST-03): Use hand vacuum pump to verify mechanical operation of wastegate actuator. Should hold vacuum and actuator rod should move smoothly.
- 7Wiring Continuity Test (Code TEST-04): Check continuity between solenoid connector and PCM connector pins using wiring diagram.
P004 Repair Procedures and Cost Analysis
P004.1 Common Repair Scenarios
| Repair Code | Repair Description | Parts Cost | Labor Time | Total Estimated Cost | Difficulty | Warranty Impact |
|---|---|---|---|---|---|---|
| R-001 | Replace Boost Control Solenoid | $75 – $250 | 0.5 – 1.0 hours | $150 – $400 | Moderate | None if OEM part |
| R-002 | Repair Damaged Wiring Harness | $20 – $50 | 1.0 – 1.5 hours | $140 – $275 | Moderate | None if proper repair |
| R-003 | Replace Wastegate Actuator | $150 – $500 | 3.0 – 6.0 hours | $600 – $1,400 | High | None if OEM part |
| R-004 | Replace Complete Turbocharger Assembly | $800 – $2,500 | 4.0 – 8.0 hours | $1,500 – $4,000 | Very High | Possible void if aftermarket |
| R-005 | PCM Reprogramming/Replacement | $100 – $1,200 | 0.5 – 2.0 hours | $200 – $1,500 | High | Dealer programming required |
P004.2 DIY Repair Instructions (Code R-001)
- 1Disconnect negative battery terminal for safety
- 2Locate boost control solenoid (refer to service manual for exact location)
- 3Document vacuum line routing with photos before disconnection
- 4Disconnect electrical connector and vacuum lines (if applicable)
- 5Remove mounting bolts (typically 2-3 bolts, 8mm or 10mm)
- 6Compare old and new solenoids to ensure correct replacement
- 7Install new solenoid and reconnect all components
- 8Reconnect battery and clear DTCs with OBD-II scanner
- 9Perform test drive to verify repair and complete drive cycle
P005 Frequently Asked Questions (FAQ)
While not immediately dangerous, we don’t recommend extended driving with P0033 active. The vehicle will likely be in a reduced-power “limp mode” which makes highway driving and merging potentially unsafe. Continued operation could also lead to more serious turbocharger damage due to uncontrolled boost pressure.
Short-term: You can drive to a repair facility or for essential trips
Long-term: Not recommended – risk of additional damage increases with mileage
Yes, potentially. An improperly functioning wastegate can lead to over-boosting or under-boosting conditions. Over-boosting creates excessive heat and pressure that can damage turbo bearings and seals. Addressing P0033 promptly can prevent more expensive turbocharger replacement.
Primary risks:
- Over-boosting causing turbine overspeed
- Excessive exhaust temperatures
- Potential engine damage from incorrect air/fuel ratios
- Catalytic converter damage from unburned fuel
Cost variation depends on several factors: the specific failed component (solenoid vs. complete turbo), whether you use OEM or aftermarket parts, your geographic location, and labor rates at the repair facility. The most common repair (solenoid replacement) is typically the most affordable.
Cost factors breakdown:
- Parts quality: OEM vs aftermarket (30-60% price difference)
- Labor rates: $80-$160/hour depending on location and shop type
- Vehicle model: Some Mers models require more labor time
- Additional repairs: Often other components are replaced preventatively
For an experienced DIYer with basic mechanical skills, replacing the boost control solenoid is often straightforward. However, proper diagnosis requires a multimeter to verify the failed component. Attempting repairs without proper diagnosis could lead to replacing good parts unnecessarily.
DIY difficulty assessment:
- Easy: Solenoid replacement on easily accessible models
- Moderate: Wiring repair or diagnosis requiring multimeter
- Difficult: Turbo removal or PCM-related issues
Disconnecting the battery may temporarily clear the code, but it will likely return once the PCM completes its monitoring cycle (typically within one drive cycle). The underlying issue must be diagnosed and repaired to permanently resolve P0033.
Drive cycle requirements: Most Mers models require 3-5 drive cycles with specific conditions (cold start, various speed ranges) to complete self-tests and confirm repairs.
