P0068 — MAP/MAF - Throttle Position Correlation

Quick answer

• What this code means: The Powertrain Control Module (PCM) has detected an inconsistency between the readings from the Manifold Absolute Pressure (MAP) or Mass Air Flow (MAF) sensor and the Throttle Position Sensor (TPS).
• Severity: Moderately severe; can lead to driveability issues and potential engine damage if ignored.
• Most common cause: A dirty or faulty throttle body or a vacuum leak.

What the P0068 code means

The official OBD-II definition for P0068 is “MAP/MAF – Throttle Position Correlation.” In simpler terms, your vehicle’s engine computer (PCM) cross-references data from several sensors to ensure everything is operating within expected parameters. The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, which is an indicator of engine load. The Mass Air Flow (MAF) sensor measures the amount of air entering the engine. The Throttle Position Sensor (TPS) monitors the opening angle of the throttle plate, indicating how much air should be entering the engine based on driver input.

When the P0068 code sets, it means the PCM has observed a discrepancy between the airflow or pressure readings (from the MAP or MAF sensor) and the commanded throttle position (from the TPS). For example, if the throttle plate is wide open (high TPS reading), the MAP/MAF sensors should report a correspondingly high airflow or low manifold pressure. If these readings don't align within the PCM's calibrated thresholds, it triggers the P0068 code, indicating a correlation issue.

This correlation is crucial for the PCM to accurately calculate fuel delivery and ignition timing, ensuring efficient combustion and performance. An incorrect correlation can lead to improper air-fuel mixture, affecting engine operation.

Common symptoms

When your vehicle sets a P0068 code, you might experience one or more of the following symptoms:

• Check Engine Light (CEL) illuminated: This is almost always the first and most obvious symptom.
• Rough idle or stalling: The engine may struggle to maintain a consistent idle speed or may completely shut off, especially when coming to a stop.
• Poor acceleration: The vehicle may feel sluggish or hesitate when you press the accelerator pedal.
• Reduced fuel economy: Incorrect air-fuel mixture can lead to the engine consuming more fuel than necessary.
• Engine surging or hesitation during driving: The engine RPMs may fluctuate unexpectedly, or the vehicle might feel like it’s briefly losing power.
• Difficulty starting: The engine might crank longer than usual or require several attempts to start.
• Black smoke from the exhaust: In some cases, an overly rich air-fuel mixture could lead to visible black smoke, indicating incomplete combustion.

Common causes

The P0068 code can stem from various issues, ranging from simple to more complex. Here are the most common causes, ranked by likelihood:

1. Dirty or faulty throttle body: Carbon buildup around the throttle plate can prevent it from closing properly, causing a discrepancy between the TPS reading and actual airflow. A faulty throttle body motor or sensor can also contribute.
2. Vacuum leaks: Leaks in the intake manifold gaskets, vacuum hoses, PCV valve, or other components can introduce unmetered air into the engine, skewing MAP/MAF sensor readings relative to the throttle position.
3. Faulty Manifold Absolute Pressure (MAP) sensor: An inaccurate MAP sensor reading will directly impact the correlation with the TPS.
4. Faulty Mass Air Flow (MAF) sensor: A contaminated or failing MAF sensor will send incorrect airflow data to the PCM, leading to a correlation error.
5. Faulty Throttle Position Sensor (TPS): If the TPS itself is providing an erratic or incorrect signal, the PCM will misinterpret the throttle's actual position.
6. Restricted exhaust system: A clogged catalytic converter or muffler can create backpressure that affects manifold pressure, indirectly impacting the MAP sensor's correlation with the TPS.
7. Problem with the PCM (Powertrain Control Module): While less common, an internal PCM fault can cause misinterpretations of sensor data and trigger this code. This is usually the last resort in diagnosis.
8. Wiring or connector issues: Damaged, corroded, or loose wiring and connectors to the MAP, MAF, TPS, or throttle body can disrupt signal integrity and lead to intermittent or constant correlation problems.

How a technician diagnoses it

Diagnosing a P0068 code requires a systematic approach to pinpoint the exact discrepancy:

1. Verify the complaint and perform a visual inspection: The technician will first confirm the illuminated Check Engine Light and search for any obvious issues like loose hoses, damaged wiring, or a dirty air filter. They will also check for any aftermarket modifications that might affect airflow.
2. Scan for trouble codes and freeze frame data: A professional scan tool will be used to retrieve the P0068 code and any other related codes. Freeze frame data, captured at the moment the code set, will provide critical information about engine conditions (RPM, engine load, temperature, etc.) that can help narrow down the problem.
3. Monitor live sensor data: The technician will monitor live data streams from the MAP, MAF, and TPS sensors with the engine running at various RPMs (idle, 2000 RPM, wide open throttle). They will look for:
   • MAP sensor readings: Should change smoothly with throttle input. At idle, typically around 18-22 inHg (60-70 kPa) for a healthy engine; should drop significantly towards 0 inHg (0 kPa) at wide open throttle.
   • MAF sensor readings: Should increase significantly with engine RPMs and throttle opening. Typical idle values range from 2-7 g/s, increasing to 80-150 g/s or more at higher RPMs/load.
   • TPS readings: Should show a smooth, linear increase from around 0.5-1.0V (or 0-20% angle) at closed throttle to 4.5-5.0V (or 80-100% angle) at wide open throttle, without any drops or spikes.
4. Test for vacuum leaks: Using a smoke machine or proper diagnostic spray (e.g., carb cleaner, propane), the technician will check all vacuum lines, intake manifold gaskets, and PCV system components for leaks. A change in engine RPM when the diagnostic spray reaches a leak indicates a problem.
5. Inspect and clean the throttle body: If carbon buildup is suspected, the throttle body will be removed and inspected. If dirty, it will be thoroughly cleaned. The operation of the throttle plate will be checked for smooth movement.
6. Test individual sensors (MAP, MAF, TPS): If live data indicates a faulty sensor, specific tests will be performed according to manufacturer specifications using a multimeter or oscilloscope to verify sensor output voltage and resistance.
   • MAP sensor: Check reference voltage (5V), ground, and signal voltage. Signal voltage should change inversely with manifold pressure.
   • MAF sensor: Check reference voltage (12V or 5V, depending on design), ground, and signal frequency/voltage. Signal should increase with airflow.
   • TPS: Check reference voltage (5V), ground, and signal voltage, ensuring a smooth, linear sweep from closed to wide-open throttle.
7. Check exhaust system backpressure: If other checks are inconclusive, the technician may use a pressure gauge to measure exhaust backpressure (e.g., by removing the upstream O2 sensor and installing the gauge). High backpressure can indicate a restricted exhaust.

Typical repair cost

The cost to repair a P0068 code can vary significantly depending on the underlying cause and your vehicle's make and model. Here are some common repair ranges:

• Cleaning the throttle body: $100 - $250 (parts are minimal, mostly labor).
• Repairing a vacuum leak: $50 - $400 (depends on the location and complexity of the leak; could be a simple hose or an intake manifold gasket).
• Replacing a MAP sensor: Parts typically range from $50 - $200; labor $50 - $150. Total: $100 - $350.
• Replacing a MAF sensor: Parts typically range from $100 - $300; labor $50 - $150. Total: $150 - $450.
• Replacing a TPS (if separate from throttle body): Parts typically range from $40 - $150; labor $50 - $150. Total: $90 - $300.
• Replacing the entire throttle body assembly: Parts typically range from $200 - $600; labor $100 - $250. Total: $300 - $850.
• Replacing intake manifold gaskets: Parts typically range from $30 - $150; labor $300 - $700 (can be labor-intensive). Total: $330 - $850.
• Replacing a restricted catalytic converter: Parts and labor can range significantly from $500 - $2,500+.

These costs are estimates and can vary based on your location and the specific repair shop.

Can I keep driving with this code?

It is not recommended to keep driving for an extended period with a P0068 code. While your car might seem to be running fine initially, the underlying issue can lead to several problems:

• Reduced performance and fuel economy: The PCM's inability to accurately determine airflow will lead to incorrect fuel delivery, resulting in poor performance and higher fuel consumption.
• Increased emissions: An improper air-fuel mixture contributes to higher levels of harmful emissions.
• Potential engine damage: If the air-fuel mixture is consistently too lean (not enough fuel) or too rich (too much fuel), it can lead to damage to critical engine components like the catalytic converter, oxygen sensors, or even internal engine parts over time. A lean condition, especially, can cause engine overheating.
• Unreliable vehicle operation: The car may stall unexpectedly or experience sudden power loss, which can be dangerous, especially in traffic.

It's best to have the issue diagnosed and repaired as soon as possible to prevent further problems and ensure your vehicle runs safely and efficiently.

Related codes

Several other codes may be related to P0068, as they often point to issues within the same sensor systems or engine components:

• P0101 - P0104: MAF/VAF Circuit Range/Performance Problems
• P0106 - P0109: MAP/BARO Sensor Circuit Range/Performance Problems
• P0120 - P0124: Throttle Position Sensor/Switch