The OBD2 code P0068 signals a discrepancy between the Mass Air Flow (MAF), Manifold Absolute Pressure (MAP), and Throttle Position Sensor (TPS) readings. This trio of sensors works together to inform the engine control module (ECM) about the air entering the engine, ensuring the fuel injection system operates efficiently. When these readings don’t align, it can lead to symptoms like erratic idle, intermittent downshifting, and rough running, as noted in the service cases.
P0068 quick overview
| Meaning | P0068: MAP/MAF – Throttle Position Correlation |
| Is it serious? | Yes, it can cause noticeable drivability issues and potentially harm engine performance. |
| Possible causes | – Faulty sensors (MAP, MAF, TPS) – Vacuum leaks in the intake system – Carbon buildup in the throttle body – Wiring or connector issues affecting sensor signals |
| How to diagnose? | Inspect the TPS, MAP, and MAF sensors for functionality and damage Check for vacuum leaks in the intake system using a smoke test Clean the throttle body to remove carbon buildup Review the wiring and connectors for any damage or loose connections Calibrate or replace the TPS if it’s found to be out of specification |
P0068 Meaning
For those less familiar with automotive lingo, imagine your car’s engine as a big air pump. The MAP and MAF sensors measure how much air is coming in, and the TPS tells the engine how hard you’re pressing on the gas.
If these measurements don’t match up correctly, as indicated by the P0068 code, your car might act up, like idling weirdly or feeling jumpy when you try to speed up. It’s akin to trying to fill a balloon with the wrong amount of air; too little and it won’t inflate properly, too much and it might pop. Fixing this issue ensures your “balloon” (or in this case, engine) operates just right.
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How to fix P0068 – learn from mechanics
I looked into P0068 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Dodge
Vehicle Information 2005 Dodge Ram 1500 ST 4.7L
Issue + Repair History
- Customer reported intermittent downshifting issues and erratic idle, particularly worse when the engine is cold.
- Previous repair history includes EGR replacement.
Other OBD2 Codes + Test Results
- P0068 (MAP/MAF – Throttle Position Correlation)
- No additional fault codes mentioned.
- Symptoms include intermittent downshifting and fluctuating idle, especially noticeable when cold.
Mechanic Suggestions
- Check Throttle Position Sensor (TPS) signal and wiring integrity.
- Inspect MAP sensor for potential issues.
- Verify correlation between MAP, MAF, and TPS readings to identify any discrepancies.
- Perform a thorough inspection of the throttle body and associated components for carbon buildup or damage.
- Ensure proper calibration and adjustment of the TPS.
Final Fix
- Replaced and calibrated the Throttle Position Sensor (TPS).
- Verified proper operation of the sensor and cleared fault code.
- Customer confirmed resolution of downshifting issues and erratic idle after TPS replacement.
Case #2: Kia
Vehicle Information 2009 Kia Rio SX 1.6L
Issue + Repair History
- Initially diagnosed with an Evap code due to a faulty purge solenoid, which was replaced under warranty.
- Subsequently, the vehicle returned with a P0068 code (MAP/TPS not corresponding) despite the replacement of the purge solenoid and installation of an OE Throttle Position Sensor (TPS).
- Thorough inspection and testing revealed no apparent issues.
- MIL lamp was off during the latest visit, but P0068 code was present in history, triggered at 43 MPH.
Other OBD2 Codes + Test Results
- P0068 (MAP/TPS not corresponding)
- No additional fault codes mentioned.
- Code triggered at 43 MPH.
Mechanic Suggestions
- Check for cracks or leaks in the intake hose connected to the MAP sensor.
- Clean the throttle body to eliminate carbon build-up, which could affect TPS/MAP correlation.
- Perform a smoke test on the intake system to detect potential air leaks.
- Verify intake vacuum readings to assess for any abnormalities.
- Investigate the possibility of a vacuum leak skewing MAP readings, causing the P0068 code.
- Consider checking vacuum with a gauge to assess the condition of the catalytic converter, especially if there are indications of potential catalyst plugging.
Final Fix
- Thoroughly cleaned the throttle body to address potential carbon build-up.
- No further recurrence of the P0068 code reported after cleaning the throttle body.
- Customer confirmed no MIL lamp illumination since the cleaning procedure.
Case #3: Chevrolet
Vehicle Information 2014 Chevrolet Cruze LT 1.4L
Issue + Repair History
- Customer complaint of rough running engine.
- Engine previously replaced due to low compression in cylinder 3.
- New engine installed, resulting in good idle, but rough running during acceleration and power reduction.
- Throttle body replaced and relearn performed, but problem persists.
- Diagnostic trouble code (DTC) P0068 (Throttle Body Airflow Performance) present.
Other OBD2 Codes + Test Results
- P0068 (Throttle Body Airflow Performance)
- No additional fault codes mentioned.
Mechanic Suggestions
- Check for vacuum leaks as they are a common cause of P0068.
- Verify vacuum leaks by removing the oil cap while the engine is running to check for vacuum in the crankcase, indicating a possible issue with the valve cover.
- Confirm that the engine replacement was done under manufacturer’s warranty.
- Investigate other potential causes such as malfunctioning Mass Air Flow (MAF) sensor, boost pressure sensor, Throttle Position (TP) sensors, and Throttle Body Injector (TBI) airflow compensation parameters.
- Ensure synchronization between throttle pedal and throttle body.
- Consider replacing the throttle body if cleaning did not resolve the issue or if there is suspicion of a vacuum leak despite no visible signs.
- Compare sensor readings with those of a known good vehicle to verify accuracy.
Final Fix
- Discovered a hairline crack in the valve cover due to front-end damage from a previous incident.
- Replaced the valve cover to address the vacuum leak, resolving the rough running engine and P0068 DTC.
- No further recurrence of the issue reported after valve cover replacement.
How to diagnose P0068
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Inspect the TPS, MAP, and MAF sensors | Check for any signs of failure or incorrect readings. |
| Check for vacuum leaks | Use a smoke test to identify any leaks that could skew sensor readings. |
| Clean the throttle body | Remove carbon buildup that might interfere with airflow and sensor accuracy. |
| Review wiring and connectors | Ensure all electrical connections are secure and undamaged. |
| Calibrate or replace the TPS | Adjust or replace the TPS to ensure it accurately reflects throttle position. |
Addressing a P0068 code typically involves a blend of electronic diagnostics to assess sensor function and mechanical checks for vacuum leaks or airflow restrictions. Given the potential for this issue to affect drivability, addressing it promptly with a thorough diagnostic process is crucial to restore engine performance and ensure smooth operation.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko