|Code||Fault Location||Probable Cause|
|P0104|| Mass air flow (MAF) sensor/volume air flow (VAF) sensor circuit intermittent |
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|Wiring, poor connection, MAFNAF sensor, ECM|
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What Does Code P0104 Mean?
The troublecode P0104 is set when the MAF sensor circuit is malfunctioning. This code is similar to P0100 – MAF sensor circuit malfunction. The difference between the two codes is the consistency of the malfunction in the MAF sensor circuit. Troubleshooting will be the same for both codes. For a P0104 code, double check wiring and connector harnesses.
When diagnosing MAF sensor codes, understanding fuel trims is very important. Please see the fuel trims article (P0171):
Identifying the type of MAF sensor in your car will also aid diagnosis. There are a number of different MAF sensors including the most common hot-wire sensors. The following Youtube video describes vane, analog or digital hot-wire, and vortex MAF sensors:
Note: Regardless of the code and the system affected, the word “Intermittent” refers to the fact that there is a sporadic, unpredictable, or, well, intermittent fault in that system. The most likely causes of codes that relate to intermittent faults include poor connections in both live and ground circuits, as well defective switches, relays, and sensors.
Intermittent faults can be extremely difficult to trace and fix, since code readers generally do not specify in which part of the circuit the problem lays. For instance, the fault could be an intermittent interruption of the reference voltage (power supply), or, as often happens, the problem could be an intermittent break in the signal voltage to the PCM (Powertrain Control Module) due to a failing sensor, wiring issues, or defective electrical connector(s).
Note that the word “intermittent” often means different things to different applications; some systems will set a code the first time an intermittent fault occurs, while others will only do so after several failure cycles. In some cases, it may be necessary to allow the fault to worsen before an accurate and definitive repair can be made.
What are the common causes of code P0104 ?
Depending on year, make, and model, DTC P0104 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 P0104 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 P0104 ?
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 P0104 ?
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.
- 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.
- Clear the DTC, shut the engine off, then turn the ignition to KOEO (Key ON, Engine OFF) position.
- 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.
- Unplug the MAF and inspect the connector for corroded or damaged pins or sockets.
- If the same DTC doesn’t come back on KOEO, the sensor internals and wiring are probably electrically sound.
- If the KOEO test doesn’t illuminate the MIL, start the engine and leave it idling.
- 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.
- 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.
- 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.