P0108 on 2015-2019 Ford Transit 3.5L EcoBoost: MAP Sensor Causes and Fixes

What's Unique About the 2015-2019 Ford Transit

The 3.5L EcoBoost engine is a twin-turbocharged, direct-injection engine that relies heavily on accurate pressure readings for performance and efficiency. Unlike naturally aspirated engines, the EcoBoost uses multiple pressure sensors: one on the intake manifold (the MAPT sensor relevant to P0108), one on the charge pipe (TCBP), and one at the turbo inlet. Due to the positive crankcase ventilation (PCV) system design, oil-laden vapor is routed into the turbocharger inlet under boost conditions. This oil vapor can travel through the intercooler and intake tract, eventually contaminating the MAPT sensor on the intake manifold, leading to faulty readings and eventual failure. This is a widely documented failure pattern on the EcoBoost platform.

Symptoms You May Notice

• Check Engine Light is on
• Powertrain Malfunction (Wrench) Light may be on
• Rough or unstable idle
• Poor engine performance and lack of power, especially sluggishness from a stop
• Hesitation during acceleration
• Reduced fuel economy
• Black smoke from the exhaust (due to rich fuel mixture)
• Engine stalling, especially when coming to a stop
• Service AdvanceTrac message on the dash
• Hill Start Assist Not Available message

Most Likely Causes

1. Faulty Manifold Absolute Pressure (MAP) Sensor 🔴 High Probability → Shop Manifold Absolute Pressure Sensor The MAP sensor on the 3.5L EcoBoost is highly susceptible to contamination from oil and fuel vapors from the PCV system, which degrades the sensor over time. Ford issued TSB 19-2212 for this exact issue on platform mates, confirming a high failure rate.
   How to confirm: With the key on and engine off, use a scan tool to compare the MAP (PRESS) PID value to the BARO (PRESS), TCBP (PRESS), and TURBO INLET (PRESS) PIDs. They should all be within 1.5 psi (10.35 kPa) of each other. If the MAP reading is significantly different, the sensor is faulty.
   Typical fix: Replace the MAP sensor located on top of the intake manifold. It is held in by a single T20 Torx screw.
   Est. part cost: $40-$100
2. Wiring or Connector Issue 🟡 Medium Probability The wiring harness in the engine bay is exposed to heat and vibration, which can lead to chafing, breaks, or corrosion in the connector pins over time. A user on a forum suspected this after a mechanic had worked in the area.
   How to confirm: Visually inspect the MAP sensor connector and wiring for any signs of damage, corrosion, or loose pins. With the connector unplugged and key on, use a multimeter to check for a 5-volt reference signal and a good ground at the connector. A technician in a YouTube video demonstrates this test on a 2016 Transit.
   Typical fix: Repair the damaged section of wire or clean/replace the connector pigtail.
   Est. part cost: $10-$30

Rare But Worth Checking

• Vacuum Leak or Cracked PCV Hose: A significant vacuum leak can cause the MAP sensor to read incorrectly. A user on the Ford Transit USA Forum with a 3.5L EcoBoost chased a similar rich condition code (P0172) and found the problem was a small, hard-to-see crack in the plastic PCV hose elbow where it connects to the intake manifold, after already replacing the MAP sensors without success.
• Clogged Catalytic Converter: A severely clogged catalytic converter can create excessive backpressure in the intake manifold, leading to an abnormally high MAP sensor reading. This is usually accompanied by other symptoms like a significant loss of power and potentially a sulfur-like smell from the exhaust.
• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is the least likely cause. The PCM is responsible for interpreting the sensor's signal. A failure within the PCM's internal circuitry could cause it to misread the data, but all other possibilities should be exhausted before considering PCM replacement.

Diagnosis Steps

1. Connect an OBD-II scanner and confirm that P0108 is the primary code. Note any other codes present, such as P0107 or P0109.
2. With the key on and engine off (KOEO), view live data on the scanner. Compare the 'MAP (PRESS)' PID to the 'BARO (PRESS)' and 'TCBP (PRESS)' PIDs. Per TSB 19-2183, they should be within 1.5 psi (10.35 kPa) of each other. If the MAP reading is high, the sensor is highly suspect.
3. Visually inspect the MAP sensor, which is located on the top of the plastic intake manifold, driver's side. Check its electrical connector for corrosion, damage, or loose pins. Inspect the nearby wiring for any signs of fraying or damage.
4. If the wiring looks good, test the circuit. Disconnect the sensor. 🎬 Watch: How to test a MAP sensor with a multimeter or scanner. With the key on, use a multimeter to verify you have a 5-volt reference on one wire and a solid ground on another.
5. If the reference voltage and ground are present, the sensor itself is the most likely cause of the problem.
6. If reference voltage or ground is missing, the problem lies in the wiring between the sensor and the PCM, or a faulty PCM (which is rare). Check for continuity on the ground wire to a known good chassis ground.
7. Before replacing the sensor, you can try cleaning it with a dedicated electronics or MAF sensor cleaner. Sometimes oil buildup is the sole cause. If cleaning doesn't resolve the issue, replacement is necessary.
8. After replacement, clear the codes with the scan tool and perform a test drive to ensure the issue is resolved.

Parts You'll Likely Need

• Manifold Absolute Pressure and Temperature (MAPT) Sensor (OEM #AA5Z-9F479-E) — This is the component that fails most frequently to cause a P0108 code on this engine, as documented in TSB 19-2212 for the same engine on other Ford platforms.
  Trusted brands: Motorcraft, Bosch, Standard Motor Products
  OEM price range: $60-$100
  Aftermarket price range: $40-$75

Related Codes That Often Appear With This One

• P0107 — P0107 is 'MAP Sensor Circuit Low Input'. Seeing both P0107 and P0108 intermittently can indicate a failing sensor or a wiring issue causing the signal to fluctuate wildly between open and shorted conditions. TSB 19-2212 covers both codes.
• P0109 — P0109 is 'MAP Sensor Circuit Intermittent'. This code often appears alongside P0107 or P0108, pointing towards a sensor that is failing or has a poor electrical connection. TSB 19-2212 also covers this code.

Technical Service Bulletins (TSBs) & Recalls

• TSB 19-2212: Supersedes 19-2183. 3.5L EcoBoost - Various Warning Indicators/Lack Of Power - DTCs P0107, P0108 And/Or P0109.
• TSB 19-2183: 3.5L EcoBoost - Various Warning Indicators/Lack Of Power - DTCs P0107, P0108 And/Or P0109.

Platform-Specific Known Issues

• Ford issued Technical Service Bulletin (TSB) 19-2212, which supersedes TSB 19-2183. It applies to 2018-2019 Explorer, Flex, Taurus, and MKT models with the 3.5L EcoBoost engine for DTCs P0107, P0108, and P0109. It identifies a faulty MAPT sensor as the cause 🎬 See this breakdown of common causes and fixes for code P0108. and recommends replacement. While the Transit is not explicitly listed, the engine, sensor part number (AA5Z-9F479-E), and symptoms are identical, making this TSB highly relevant.

Mechanic-Grade Diagnostic Values

• MAP Sensor 5V Reference Voltage — expected: Approximately 5.0 Volts DC. Failure: No voltage or significantly lower voltage indicates a wiring or PCM issue.
• MAP Sensor Signal Voltage (KOEO - Key On, Engine Off) — expected: Approximately 4.5V to 5.0V (reading atmospheric pressure).. Failure: Voltage significantly lower than 4.5V or 0V suggests a sensor or wiring fault.
• MAP Sensor Signal Voltage (Engine Idling) — expected: 2.0V to 2.5V for turbocharged models.. Failure: A P0108 is set when voltage remains above the expected range, often over 4.4V-4.5V at idle.
• MAP Sensor Signal Frequency (Older Fords, KOEO) — expected: Approximately 158 Hz at sea level.. Failure: A reading that is significantly different or does not change with vacuum applied.
• Wiring Continuity Test — expected: Less than 0.5 Ohms. Failure: A reading of 'OL' (Open Loop) indicates a break in the wire. A reading higher than 0.5 Ohms indicates high resistance.

Scan Tool Commands That Help

• Ford IDS (Integrated Diagnostic System): Datalogger - PID comparison — To simultaneously monitor the MAP, BARO, and TCBP sensor values during KOEO and KOER tests to see if the MAP sensor reading is skewed compared to the others, which is a primary confirmation method per Ford TSBs.

Wiring & Ground Locations

• Main Engine/Chassis Ground — On the MK7/V363 platform, there is a primary ground strap from the gearbox to the inner wing below the under-hood fuse box.. A poor main engine ground can cause floating voltages and erratic sensor readings across the entire engine management system, including the MAP sensor. Ensuring this connection is clean and tight is a crucial preliminary step.
• B-Pillar Ground Point — A factory ground point is located on the B-Pillar, often near the D-ring.. While not directly for the MAP sensor, this is a known, reliable chassis ground point. When testing the MAP sensor's ground wire for continuity, this is a good reference point to use with a multimeter.
• MAP Sensor Connector Pins — At the sensor on top of the intake manifold.. Testing must be done at the correct pins. Pin assignments can vary, but generally consist of a 5V reference wire, a signal wire, and a ground wire. A wiring diagram is needed to confirm which pin is which for accurate testing.

Real Owner Repair Stories

• Ford F150 Forum (2011 Ford F-150 3.5L EcoBoost) — Uneven running at wide-open throttle, multiple MAP-related codes (P0098, P0106, P0108) appeared after replacing the top MAP sensor.
  ❌ Tried (didn't work) Replacing spark plugs and coil packs, Replacing the top MAP sensor (which triggered the codes), Reinstalling the old MAP sensor, Replacing the charge pipe MAP sensor
  ✅ What actually fixed it The owner found frayed wires on the Turbocharger Control Valve (TCV) connector. After repairing that connector, the issue was resolved. This highlights that wiring issues on nearby components can sometimes induce faults or symptoms that appear to be MAP sensor-related.

OEM Part Supersession History

• 2R3Z-9F479-AA → AA5Z-9F479-A — Part revision and update by Ford.
• AA5Z-9F479-A → AA5Z-9F479-E — This is the current, most updated part number recommended by Ford TSBs to resolve the P0108 issue. It is also sold under service part numbers CX-2228 and CX-1876.
  Heads up: Using older, superseded part numbers may lead to a repeat failure, as the TSBs point to a flaw in the original sensor design that the newer revisions aim to correct.

Diagnostic Flowchart

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0107 — Manifold Absolute Pressure/Barometric Pressure Circuit Low Input. Often appears alongside P0108 and is explicitly grouped with it in TSB 19-2212 and TSB 19-2183 for MAPT sensor failures.
• P0109 — Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent. Also grouped with P0108 in TSB 19-2212 and TSB 19-2183 for the same MAPT sensor failure.
• P0172 — System Too Rich (Bank 1). Can occur if the faulty MAP sensor causes over-fueling (black smoke), or due to a cracked PCV hose mimicking MAP/air issues.
• P0175 — System Too Rich (Bank 2). Similar to P0172, caused by over-fueling from bad MAP data or PCV vacuum leaks.
• P0401 — Exhaust Gas Recirculation Flow Insufficient Detected. Appeared alongside P0108 in a 2017 Transit owner's report regarding acceleration struggles.

Frequently Asked Questions