P1104
SubaruThe Powertrain Control Module (PCM) detects an incorrect or open ground circuit condition for the Mass Air Flow (MAF) sensor.
Medium SeverityThis code indicates that the vehicle's computer has detected an issue with the ground circuit for the Mass Air Flow (MAF) sensor. This electrical problem prevents the MAF sensor from sending accurate air intake data to the engine, potentially leading to poor engine performance and reduced fuel efficiency.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical work to prevent shocks or damage to the electrical system. Allow the engine to cool before working on any engine components to avoid burns. Wear appropriate safety glasses.
Common Symptoms
- Check Engine Light illuminated
- Rough idle
- Engine hesitation during acceleration
- Decreased fuel economy
- Poor engine performance
- Stalling
Common Causes
- Corroded or loose MAF sensor ground wire
- Damaged MAF sensor wiring harness
- Faulty MAF sensor
- PCM internal ground circuit issue (less common)
Frequently reported on: Subaru Impreza 2000-2007, Subaru Forester 1998-2008, Subaru Legacy 1999-2004, Subaru Outback 1999-2004
Diagnostic Steps
- Inspect the Mass Air Flow sensor connector and wiring harness for any visible damage, corrosion, or loose connections, especially the ground wire.
- Clean the MAF sensor connector pins using electrical contact cleaner.
- Verify the MAF sensor's ground circuit integrity using a multimeter. Look for continuity to a known good chassis ground.
- If the wiring appears intact and the ground is good, try cleaning the MAF sensor element with specialized MAF cleaner.
- Clear the code and test drive the vehicle to see if the issue recurs.
👨🔧 When to Call a Professional
If you lack experience with electrical diagnostics, or if basic checks do not resolve the issue, it is highly recommended to consult a professional mechanic. Ground circuit issues can be complex to pinpoint without specialized tools.
Commonly Asked Questions
What does a MAF ground malfunction mean?
It means the Powertrain Control Module isn't getting a proper ground signal from the Mass Air Flow sensor, leading to incorrect air intake readings.
Can I drive with a P1104 code?
While you might be able to drive, it's not recommended as it can cause poor engine performance, reduced fuel economy, and potentially other engine issues over time.
Is cleaning the MAF sensor enough to fix this code?
Cleaning the sensor can help if it's dirty, but P1104 specifically points to a ground issue, so electrical checks are more critical.
How do I test the MAF sensor ground?
Using a multimeter, check for continuity between the MAF sensor's ground wire terminal (refer to a wiring diagram) and a known good chassis ground point with the ignition off.
Could a bad MAF sensor cause a P1104?
Yes, an internal fault within the MAF sensor itself could cause an open ground circuit or incorrect ground readings, leading to this code.