P0068 – Meaning, Causes, Symptoms, & Fixes
Code P0068 Definition
There is a difference between the Manifold Absolute Pressure (MAP), Mass Air Flow (MAF), and Throttle position sensor (TPS) voltage values.
What Does P0068 Mean?
The ECM relies on the input from the mass airflow (MAF) to determine how much air is being ingested into the engine, the throttle position sensor (TPS) to determine how much the throttle body is being opened, and the manifold absolute pressure sensor to determine what the pressure is inside the intake manifold. When this code is set, the ECM is seeing an irregular voltage from these sensors and determining that there is a fault-based on programmed rationality.
What Are The Symptoms Of Code P0068
- Check Engine Light
- Hard/No Start
- Rough Idle
- Hesitation On Acceleration
- Lack Of Power
*No noticeable adverse conditions in some cases
What Is The Cause Of Code P0068?
- Vacuum leak
- Dirty air filter
- Intake air leak
- The clogged or disconnected line to MAP sensor
- Carbon buildup on the throttle body
- Faulty mass airflow sensor
- Dirty mass airflow sensor
- Faulty manifold absolute pressure sensor
- A faulty throttle position sensor
- Poor electrical connections at sensors
How Serious Is Code P0068? – Severe
This trouble code can cause some pretty severe driveability concerns and may make the vehicle undrivable. It can also affect how efficiently the engine runs and cause damage to the catalytic converter(s).
Code P0068 Common Diagnosis Mistakes
The most common diagnosis mistake is the replacement of sensors without inspecting for any vacuum or intake leaks.
Tools Needed to Diagnose:
- Basic hand tools
- Mass airflow cleaner
- Throttle body cleaner
How To Diagnose And Repair Code P0068?
Difficulty of Diagnosis and Repair (3 out of 5)
- Check to see if there are any other codes along with P0068 and clear your Check Engine Light with FIXD. If there are any other MAF, MAP, or TPS related codes, diagnose them first before diagnosing code P0068.
- Check the freeze frame data in order to pinpoint the issue.
- Check the condition of the air filter and replace it if it’s dirty.
- Conduct a visual inspection of wiring and connectors at the MAP, MAF, and TPS for fraying, disconnection, or poor pin fitment.
- Conduct a visual and audible inspection of the vacuum lines and any intake connections to make sure there are no signs of disconnection or outside air leaks. (This includes the intake pipe between the throttle body and MAF).
- Listen for a hissing sound which can be a sign of a vacuum leak.
- Spray water over intake area and listen for idle rpm stumble. If it goes down, there is an intake leak. Concentrate the stream on different hoses and gaskets until you find your leak.
- Check the Mass Air Flow sensor to make sure that it’s not dirty and possibly putting out false readings which affect the O2 sensor. If it is dirty, clean it, clear your codes using the FIXD device, and re-scan to see if the code is still triggered.
- Remove the intake pipe from the throttle body and inspect the throttle body for carbon build-up. If it is dirty, clean it, clear the codes using the FIXD device, and re-scan to see if the code is still triggered. Tech Tip: DO NOT spray the throttle body with the cleaner, spray it on a rag and wipe the butterfly surfaces and housing clean.
- If the manifold absolute pressure sensor is mounted remotely from the intake manifold, verify that air passes through the vacuum line feeding it.
- If at this point the code is still populating, you will need to check the three sensors in question, TPS, MAF, and MAP.
- How To Check The Throttle Position Sensor. Back probe the TPS sensor connector with the connector plugged in and the key on engine off. One wire should have battery voltage. (usually a red wire). One wire will have close to no voltage (usually a black wire and should be less the 100mV). The other wire should have .5 or so volts with the throttle closed and a little less than 5 volts with it wide open. It should also steadily increase as you slowly open the throttle. If it jumps or dips, replace the throttle position sensor.
- How To Check The Mass Air Flow Sensor. Back probe the MAF sensor connector with the connector plugged in and the key on engine off. One wire should have battery voltage. (usually a red wire). One wire will have close to no voltage (usually a black wire and should be less the 100mV). One wire is for the intake temp sensor if so equipped (this will not be tested for this code). The last wire will be our signal wire. Start the engine and monitor this voltage. It should change with engine RPM.
- How To Check The Manifold Absolute Pressure Sensor. Back probe the MAP sensor connector with the connector plugged in and the key on engine off. One wire should have battery voltage. (usually a red wire). One wire will have close to no voltage (usually a black wire and should be less the 100mV). The other wire should have 4.5 to 5 volts key on engine off. Now, start the engine and it should drop to between .5 and 1.5 volts depending on altitude and temperature. Raise the engine rpm. The voltage should react to the throttle opening by dropping and rising again. If not, replace it.
- Hopefully, at this point, you have found your problem. If the code persists, you may need to take it to a shop to have it diagnosed.
Estimated Cost of Repair
For error code P0068, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.
- Fix Intake/Vacuum Leak $150-$250
- Wiring repair/replacement $100-$1000
- Air filter $20
- Throttle position sensor $170-$230
- Throttle body cleaning $230-$290
- Manifold absolute pressure sensor $150-$200
- Mass airflow sensor $300
- Clean mass airflow $100