P0101 – Mass air flow (MAF) sensor/volume air flow (VAF) sensor range/performance problem

By Benjamin Jerew (Contact Me)
Last Updated 2018-06-08
ASE Master Tech

Table of Contents

1. What Does Code P0101 Mean?
2. What are the common causes of code P0101?
3. What are the symptoms of code P0101?
4. How do you troubleshoot code P0101?
5. Get Help with P0101

What Does Code P0101 Mean?

An engine needs three things to run – air, fuel, and spark. To deliver the most efficient power, a precise amount of fuel needs to be injected into the cylinder, after which it is compressed and ignited, resulting in a power stroke. Ideally, the air-fuel ratio is 14.7:1, though this can vary depending on engine speed (RPM), engine load, coolant temperature, intake air temperature, and intake air mass. To measure how much air is coming into the engine, many modern engine controllers (PCM or ECU) use a Mass Air Flow (MAF) sensor, typically simply referred to as the MAF.

When the engine is running, air passes through the MAF, which sends a voltage signal to the engine controller. The voltage varies, depending on how much air is passing through the sensor. The ECU expects the MAF signal to be within a certain range, depending on RPM and load. If the MAF signal goes outside of this range, higher or lower voltage than expected, the ECU ignores it and sets a diagnostic trouble code (DTC), P0101. This generic onboard diagnostic system (OBDII) DTC refers to Mass Air Flow (MAF) Circuit Range / Performance.

Note: A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors. The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with these codes, it is important to regard all sensors and components as part of the control circuit the code refers to.

What are the common causes of code P0101?

Depending on year, make, and model, DTC P0101 may have a number of causes. Here are some of the most common.

• Toyota / Lexus – The hot-wire MAF sensor is notoriously susceptible to oil contamination and aftermarket air filter contamination. Cleaning may work, but replacement of the MAF sensor and an OEM (original equipment manufacturer) air filter are a sure fix.
• Cars over Ten Years Old – Over time, the rubber hoses can become brittle, cracking where it should flex. Do a thorough check on all rubber hoses, from vacuum lines to the intake tube.
• General Motors – Some vehicles, with a heavily contaminated catalytic converter, may set this DTC. Do an engine vacuum test
• Volkswagen / Audi vehicles
• Vehicles in Storage – Check wiring harnesses and air intake systems for rodent infestation and damage. Mouse nests are not uncommon in stored vehicles, and they tend to build their nests in inaccessible places, such as the air intake tubing. To build their nests, they seem to have a liking for air filter and noise deadening materials, which can easily clog the intake system or contaminate the MAF. Mice also seem to have a taste for rubber hoses and electrical insulation, and chewed-through hoses and wires are a common issue.
• Cars with EGR Valves – Some EGR (exhaust gas recirculation) valves, over time, may become carbon-contaminated, sticking open and adversely affecting intake air flow, leading to this DTC.
• Faulty PCV Valve – A fault PCV (positive crankcase ventilation) valve may allow too much air from the crankcase into the intake tube. Depending on where the PCV inlet is, it may simply introduce too much air, or contaminate the air filter and MAF with oil.
• Faulty MAP Sensor – Some cars may use a MAP (manifold absolute pressure) sensor in conjunction with the MAF. If the MAP is faulty, this may throw off the accepted-values table for the MAF, leading to this DTC, even if there is nothing wrong with the MAF. As always, check and repair any concurrent DTCs.

Generally-speaking, if something looks out of place, then it probably is. In the case of a MAF sensor, contamination can just as easily set DTC P0101 as can a split intake tube. Usually, best practice dictates starting with the simplest and least expensive repair first. If an alcohol bath and a new air filter solves your MAF contamination problem, then you’ll save yourself a few hundred dollars. On the other hand, if you can eliminate broken vacuum lines, corroded electrical connections, and clogged air intake tubing, you can spend the money on a new MAF with confidence.

What are the symptoms of code P0101?

The ECU will also illuminate the MIL (malfunction indicator lamp), also referred to as the CEL (check engine light), though you may not notice any drivability issues. Still, aside from the MIL, some common symptoms may include difficulty starting, poor idle quality, or lack of power. Additionally, since the MIL indicates that the ECU is now running the engine in open-loop “limp home mode,” you may also notice poor fuel economy.

How do you troubleshoot code P0101?

In the intake air stream, the MAF is located somewhere between the air filter box and the intake manifold, some models placing the sensor right on the air filter box, and others in the intake hose. Depending on if the MAF has an integrated IAT (intake air temperature) sensor, it may have between four and seven wires coming out of it. The following troubleshooting steps should be taken to confirm failure and make a proper repair.

1. If you can save or print freeze frame (FF) data, taking note of important FF data points, such as RPM, vehicle speed, and gear position. Try to recall driving conditions, as well as any recent maintenance or repairs, when the MIL came on the first time. All of these can give you clues as to when the problem is occurring. Concurrent DTCs should also be noted, especially if they are related to the Fuel and Air Metering System, such as P0171 or P0111.
2. Clear the DTC, shut the engine off, then turn the ignition to KOEO (Key ON, Engine OFF) position.
   1. If the same DTC comes back immediately, chances are that you have a hard fault, perhaps a broken wire, dead sensor, or unplugged sensor. If this is the case, take a look at the connector and wiring going to the MAF.
   2. Unplug the MAF and inspect the connector for corroded or damaged pins or sockets.
   3. If the same DTC doesn’t come back on KOEO, the sensor internals and wiring are probably electrically sound.
3. If the KOEO test doesn’t illuminate the MIL, start the engine and leave it idling.
   1. If MIL illuminates during the KOER (Key ON, Engine RUNNING) test, with the same DTC, suspect the MAF sensing portion of contamination or blockage. Take out the MAF and inspect it with a flashlight. Blow out any dust or debris which may be blocking the sensing portion. If you suspect oil contamination or similar, you can attempt to clean it in a bath of isopropyl alcohol (90% or better), electrical contact cleaner, or MAF sensor cleaning spray. Do not attempt to brush or scrub the sensing portion, as it can be extremely fragile. Even so, excessive contamination may be impossible to clean, even after multiple applications, and replacement may be the only option.
   2. A concurrent fuel trim DTC, such as P0171, may point to an intake leak or vacuum leak. In either of these cases, more air is getting into the engine than the MAF and ECU can properly account for. Look for loose or cracked vacuum lines, including those to the vacuum brake booster or power steering idle-up switch. Also check the intake air hose after the MAF, making sure there are no holes or cracks.
4. If the KOER test is inconclusive, taking the car for a test drive may be necessary. If you were able to glean any important information from the FF data, try to reproduce the driving conditions during which the fault was detected. Lack of power and an illuminated MIL on hard acceleration might point to a cracked intake hose, for example.

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