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The manifold absolute pressure (MAP), mass airflow (MAF), and throttle position (TPS) sensors keep track of the engine’s air intake in different ways. The MAP sensor measures the air pressure in the intake manifold, while the similarly-named but different MAF sensor calculates the engine’s airflow volume and the TPS sensor shows the position of the throttle plate in the throttle body.

For probably twenty years now, engineers have built algorithms into engine control software to do what is called “rationality checks.” If, for example, the engine is believed to be at idle base on throttle position sensor input and the mass airflow input doesn’t increase when the ECM/PCM increases idle air control percentage to raise the idle speed, the ECM/PCM is programmed to see that as an anomaly. Likewise, if the throttle position sensor indicates that the throttle plate is being opened but the mass airflow input doesn’t show a corresponding increase in airflow, that’s an anomaly that will set a code.

A discrepancy in the readings from these sensors can contribute to a code P0068. To learn more about this error code, check out our guide below.

What Does the P0068 Code Mean?

Diagnostic trouble code (DTC) P0068 stands for “MAP/MAF – Throttle Position Correlation.” If the readings from one or more of these sensors contradict the data presented by the other devices, the vehicle’s computer, aka the powertrain control module (PCM), logs the OBD-II trouble code P0068.

throttle position sensor
A discrepancy in the readings from the MAP, MAF, and TPS sensors can trigger code P0068.

The criteria for this code will vary from one OEM to the next, but to calculate an expected airflow rate, the GM algorithm uses:

  • The throttle position (TP)
  • The barometric pressure (BARO)
  • The manifold absolute pressure (MAP)
  • The intake air temperature (IAT)
  • The engine RPM

The mass air flow, manifold absolute pressure, and the throttle position sensors provide the rationality check inputs, but there are 4 separate algorithm models on 2017 GM vehicles. The way those algorithms are calculated isn’t as important as developing an understanding of what rationality checks are all about, particularly when looking at live scan tool data.

The PCM regularly tests the inputs in play by comparing the sensor readings. The reading from each sensor should correspond to the equivalent data on the other sensors—otherwise, the PCM may log a P0068 code.

The readings from these sensors guide the PCM when it sets how long the fuel injectors stay open and when the spark plugs trigger to ignite the resulting fuel-air mix inside the engine. It will tweak these variables to achieve the most efficient fuel-to-air ratio.

Note: While the Society of Automotive Engineers (SAE) established the generic code P0068, the vehicle’s manufacturer may come up with a different interpretation for the code.

What are the Possible Causes of the P0068 Code?

The PCM can set a P0068 code for various reasons. These issues include the following:

map sensor
A bad or failing MAP sensor can cause code P0068.

What are the Common Symptoms of the P0068 Code?

If one or more of these sensors sends inaccurate signals to the PCM, the computer may send the wrong amount of fuel or activate the ignition system at the wrong time.

An affected vehicle will display the following warning signs related to code P0068:

  • Illuminated check engine light
  • Rough engine performance (e.g., rough idling or poor acceleration)
  • Increased fuel consumption

The PCM can also set other codes associated with whatever developed the problem. For example, a faulty MAF sensor may trigger a P1101 code along with a P0068.

How to Diagnose the P0068 Code

If your scan tool turns up a P0068 code, bring your vehicle to a reliable auto repair shop and get an experienced mechanic or technician to look it over.

However, if you have the skills and tools to diagnose it yourself, here are some of the diagnosis steps you can try in order to figure out the underlying problem:

  • Check for leaks or loose clamps in the piping from the MAF sensor to the throttle body
  • Inspect the connectors of the MAP, MAF, and throttle position sensors for corrosion and other visible issues
  • Fire up the engine and test the intake manifold for leaks
  • Check for signs of coke (a greasy, dark-colored material) inside the throttle body
  • Run tests on each sensor to make sure they all work properly
mass air flow sensor
Checking for leaks in the piping of the MAF sensor to the throttle body is one possible way to diagnose code P0068.

How to Fix the P0068 Code

There is no one-size-fits-all solution to resolve the P0068 code. The sheer number of possible causes that trigger the code makes it difficult to find the right fix.

A professional mechanic should be able to handle the job for you.

However, if you feel like you have the necessary tools and automotive DIY skills, you can give it a try. You will need the help of online guides or repair manuals, though, to make sure you’re following the right repair process for your vehicle.

Just remember that what might work for one car may not work for another vehicle made by a different manufacturer.

Products Mentioned in this Guide

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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