Your vehicle has various sensors that perform different functions. The mass air flow (MAF) sensor is one of them, and it is used to measure the air that enters the engine so the powertrain control module (PCM) knows how much fuel is needed to operate the vehicle.
When trouble code P0104 is stored, it means there is an intermittent problem within the MAF circuit. Learn more about what code P0104 means, what causes it, and how you can fix it.
What Does Code P0104 Mean?
The P0104 code stands for “Mass Air Flow (MAF) “A” Circuit Intermittent/Erratic.” DTC P0104 is one of several codes in your vehicle’s On-Board Diagnostics II (OBD-II) system that indicate a problem with the MAF sensor circuit.
Ford describes this code as “a concern [that] exists in the MAF sensor A circuit or the air tube containing the sensor, causing an incorrect airflow reading.”
The MAF sensor, which is mounted on the vehicle’s engine air intake tract between the air filter and the throttle body, measures the volume and density of air drawn into the engine. It sends this reading to the PCM and the computer uses the value to ensure accurate fuel delivery.
If the MAF sensor malfunctions and sends erratic or intermittent signals, code P0104 will be set. The code may also appear when the PCM detects a MAF sensor frequency signal that is not within the normal expected range of the calculated MAF value.
As a generic engine code, P0104 can be set in any car brand or by any manufacturer, such as Ford and Chevy.
What Causes Code P0104?
Intermittent faults can be difficult to accurately pinpoint, since code readers normally do not specify which part of the circuit is problematic. For instance, the problem could be sporadic interruption to the power supply, or, as is often the case, could be an intermittent break in the signal voltage to the PCM due to a failing sensor, wiring issues, or defective electrical connectors.
So, the issue could be something as simple as a crack in the intake tube (such as the one in the photo below) that opens up when you apply the throttle and the engine torques on its mounts.
A number of reasons can cause the error code P0104 to be stored. The common ones are:
- Contaminated or damaged MAF sensor
- Debris between the air filter and MAF sensor
- Intake air leaks
- MAF sensor wiring issues
- Faulty PCM
Contaminated or Damaged MAF Sensor
A contaminated sensor can send incorrect airflow data to the PCM. Dirt, debris, or oil buildup on the sensor disrupts its ability to measure incoming air accurately, potentially leading to erratic readings. This typically happens when the air filter is cheap or torn and lets dirt through. Some of the crud gets through the filter and cakes on the sensor, as well as the hot and cold wires.
Meanwhile, a physically damaged MAF sensor may generate erratic signals or no signal at all. Common causes include internal electrical failure, exposure to water, or physical impact.
Debris Between the Air Filter and MAF Sensor
Many MAF sensors have a screen, and if dirt or debris (like a stray leaf) is lying between the air filter and the MAF sensor, it can trigger this code along with stumbles and lean pinging.
Intake Air Leaks
Leaks in the intake system (including the air inlet tube shown in the photo above) allow unmetered air to enter, creating discrepancies between actual airflow and MAF sensor readings.
MAF Sensor Wiring Issues
Faulty wiring, corroded connectors, or broken pins in the MAF sensor circuit can cause intermittent or no signal to the PCM.
Faulty PCM
A defective PCM can misinterpret signals from the MAF sensor, even if the sensor itself is functioning correctly.
In the case of a GM vehicle, this code can be stored when a cheap whitebox aftermarket sensor is used, even if the frequency is within limits. Note that GM uses frequency, while Ford uses voltage. Both provide the same information: how many grams per second of air enters the intake through the throttle body.
What Are the Symptoms of Code P0104?
One of the most common symptoms of code P0104 is an open check engine light. Here are other, more specific symptoms you should also look out for:
- Engine stalling
- Rough running engine
- Black smoke from the tailpipe
- Hard starting
- Other drivability symptoms or none at all
Engine Stalling
Engine stalling happens when the PCM receives incorrect airflow data, disrupting the air-fuel mixture. This can cause the engine to shut off suddenly, especially during idling or low-speed conditions.
Rough Running Engine
A rough-running engine may result from an inaccurate air-fuel ratio caused by faulty MAF sensor readings. This can lead to misfires, vibrations, and uneven performance.
Black Smoke From the Tailpipe
Black smoke from the tailpipe indicates an overly rich air-fuel mixture, which can happen when the MAF sensor sends inaccurate readings. The engine compensates by injecting excess fuel, leading to inefficient combustion.
Hard Starting
Hard starting happens when incorrect airflow data prevents the PCM from delivering the proper amount of fuel during startup. This results in delayed ignition or multiple attempts to start the engine.
Other Drivability Symptoms or None At All
In some cases, drivability issues like hesitation, surging, or reduced power may occur, but symptoms may also be minimal or completely absent. The severity depends on how the PCM compensates for the erratic MAF sensor data.
How to Diagnose Code P0104
Attempting to diagnose code P0104 may seem like a difficult task if you’re a beginner, but it should be relatively straightforward. Here are some troubleshooting steps you can try to diagnose the root of code P0104:
Review All Stored DTCs
The location of the OBD-II port varies depending on the vehicle, but it’s commonly found under the dashboard on the driver’s side. Once plugged in, the scanner will display all stored DTCs. Review and take note of the stored codes to help determine the root of the issue.
Conduct a Visual Inspection of the Air Filter
Locate the air filter in the engine bay, then unclip or unscrew the cover to gain access to it. Take the filter out and inspect it for dirt, debris, or oil contamination.
Check for damage such as tears or holes as well.
Conduct a Visual Inspection of the MAF Sensor Wiring
Check that all MAF sensor cables and connectors are undamaged, not twisted, frayed, or routed too close to motors, relays, ignition wires, or coils, etc. Also, check for signs of contamination.
Check for Leaks in the Air Intake System
Check for signs of physical damage, corrosion, or leaks in the air intake system.
Check for Bad PCM
If the sensor and wiring are in good condition, check for proper voltage and ground at the PCM harness; if all signals are within specifications but the PCM fails to respond or provides erratic data, it may indicate a faulty PCM.
How to Fix Code P0104
Once you’ve determined the root cause of the P0104 error code, it’s time to fix the issue. Keep in mind that there’s no single solution for OBD-II codes. That said, here are some common fixes for the P0104 code:
Clean or Replace the MAF Sensor
A contaminated MAF sensor can cause intermittent signals. Cleaning the sensor with an appropriate cleaner or replacing it can resolve the issue.
Repair or Replace Faulty Wiring or Connectors
Damaged wiring or corroded connectors affect the signal between the MAF sensor and PCM. Replacing the faulty wires ensures proper signal transmission.
Replace Dirty Air Filter
A clogged air filter can affect airflow readings. Replacing the air filter should fix the issue, but as previously mentioned, a low-quality filter can lead to the contamination of the MAF sensor. Therefore, make sure to purchase a quality replacement.
Seal Vacuum Leaks
Vacuum leaks can let unmetered air in, causing erratic MAF readings. Sealing these leaks stabilizes airflow measurements.
Update or Replace PCM
Although rare, a failing PCM can misinterpret or fail to process the sensor's signals correctly. If all other potential issues are ruled out, updating or replacing the PCM may be necessary.
Other Codes Related to P0104
Other codes related to P0104 involve errors with the transmission range sensor. These are some related codes that could also appear:
P0100
Code P0100 indicates a general malfunction in the MAF sensor circuit. The PCM is receiving no signal, an incorrect signal, or one outside the expected range.
P0101
Error code P0101 occurs when the MAF sensor readings are outside the expected range for current engine conditions.
P0102
Trouble code P0102 means the PCM has detected a low signal from the MAF sensor, typically caused by a dirty sensor, a clogged air filter, or electrical problems.
P0103
This code indicates the MAF sensor is sending a signal higher than expected.
FAQ
Is it okay to drive if the MAF sensor is bad?
No, driving with a malfunctioning MAF sensor is not advised. This is because a faulty MAF sensor results in poor acceleration, rough idling, decreased fuel efficiency, and possible stalling—all affecting drivability and necessitating immediate replacement.