P0108 on 2018-2019 Ford Flex 3.5L EcoBoost: MAP Sensor Causes and Fixes

What's Unique About the 2018-2019 Ford Flex

For this specific vehicle and engine, the P0108 code is very well-documented. Ford issued Technical Service Bulletins (TSB 19-2183, later superseded by 19-2212) for the 2018-2019 Flex, Explorer, Taurus, and Lincoln MKT with the same 3.5L EcoBoost engine. The TSBs acknowledge that a faulty Manifold Absolute Pressure and Temperature (MAPT) sensor is the likely cause for this code, often appearing alongside P0107 (low input) and P0109 (intermittent). This makes diagnosis much more direct than on other vehicles where the cause could be a vacuum leak, wiring issue, or even a clogged catalytic converter.

Symptoms You May Notice

• Illuminated Check Engine Light (Malfunction Indicator Lamp)
• Powertrain Malfunction (Wrench) Light
• Significant lack of power and sluggish acceleration
• Service AdvanceTrac message
• Hill Start Assist Not Available message
• Rough or unstable idle
• Poor fuel economy
• Black smoke from the exhaust
• Hesitation or stalling when accelerating from a stop

Most Likely Causes

1. Faulty Manifold Absolute Pressure and Temperature (MAPT) Sensor 🔴 High Probability → Shop Manifold Absolute Pressure Sensor This is a widely known failure point documented by Ford in TSB 19-2183 and 19-2212 for this specific vehicle, engine, and year range. The sensor is a combined unit that measures both pressure and temperature, and it is prone to internal failure.
   How to confirm: Use a scan tool with the Key On, Engine Off (KOEO). Compare the MAP (PRESS) PID to the BARO (PRESS), TCBP (PRESS), and TURBO INLET (PRESS) PIDs. Per the TSB, if the MAP reading is more than 10.35 kPa (1.5 psi) different from the others, the sensor is faulty. The presence of codes P0107 or P0109 further confirms a bad sensor.
   Typical fix: Replace the MAPT sensor. It is located on top of the intake manifold and held by a single T20 Torx screw. The engine cover must be popped off for access. 🎬 See this walkthrough for replacing the sensor on a Flex. After disconnecting the electrical connector, the old sensor may require a gentle back-and-forth twisting motion to break the O-ring seal before it can be pulled out. Lubricating the new sensor's O-ring with clean engine oil can ease installation.
   Est. part cost: $90-$190
2. Wiring or Connector Issue ⚪ Low Probability While less common than outright sensor failure on this platform, engine heat cycles can make wiring brittle over time. The connector itself can also be damaged or develop corrosion. However, the TSB-documented high failure rate of the sensor itself makes this a secondary check.
   How to confirm: Visually inspect the MAPT sensor connector and its wiring harness for any signs of damage, corrosion, or loose pins. With the sensor disconnected and key on, use a multimeter to check for a 5-volt reference signal and a good ground at the connector. A 'wiggle test' on the connector while monitoring live data can sometimes reveal an intermittent connection.
   Typical fix: Repair the damaged section of wiring or replace the connector pigtail.
   Est. part cost: $15-$40

Rare But Worth Checking

• Clogged Catalytic Converter: A severely restricted exhaust can cause an increase in manifold pressure, potentially triggering a P0108 code. This is unlikely to be the primary cause without other symptoms like a significant loss of top-end power and potentially other exhaust-related codes.
• Powertrain Control Module (PCM) Failure: → Shop Engine Control Module (ECM) This is extremely rare. The PCM is the last item to suspect after all other possibilities, including the sensor and its entire circuit, have been thoroughly tested and ruled out.

Diagnosis Steps

1. Connect an OBD-II scanner and confirm the P0108 code is present. Note any other codes, especially P0107 and P0109, as their presence strongly indicates the MAPT sensor is the root cause per Ford's TSB.
2. With the Key On and Engine Off (KOEO), use the scanner's live data function to view the Manifold Absolute Pressure (MAP) PID and the Barometric Pressure (BARO) PID.
3. Per Ford TSB 19-2212, compare the MAP (PRESS) PID to the BARO (PRESS), TCBP (Turbocharger Boost Pressure), and TURBO INLET (PRESS) PIDs.
4. If the MAP reading differs by more than 1.5 psi (10.35 kPa) from the other pressure sensors, the MAPT sensor is confirmed to be faulty and must be replaced.
5. If the sensor readings seem plausible, visually inspect the MAPT sensor connector and wiring for damage, corrosion, or loose pins.
6. If wiring looks good, test the circuit. Check for a 5-volt reference and good ground at the connector. Test the signal wire for continuity back to the PCM.
🎬 Watch: How to test and replace a faulty MAP sensor.
7. If the sensor and wiring are confirmed to be good, investigate rarer causes like a restricted exhaust.

Parts You'll Likely Need

• Manifold Absolute Pressure and Temperature (MAPT) Sensor (OEM #AA5Z-9F479-E) — This is the confirmed cause of the issue in the vast majority of cases, as documented by Ford's own Technical Service Bulletins (19-2183, 19-2212). This part number is the specific replacement called for in the TSB. It supersedes previous versions like AA5Z-9F479-A and 2R3Z-9F479-AA. This is a 3-bar sensor designed for the EcoBoost engine.
  Trusted brands: Motorcraft (OEM), Standard Motor Products, Bosch
  OEM price range: $90-$190
  Aftermarket price range: $50-$120

Related Codes That Often Appear With This One

• P0107 — This code for 'MAP Circuit Low Input' often appears with P0108 when the sensor is failing intermittently, as documented in Ford's TSB.
• P0109 — This code for 'MAP Circuit Intermittent' also points directly to a failing sensor, as the signal is dropping out or providing erratic readings.

Technical Service Bulletins (TSBs) & Recalls

• TSB 19-2212: '3.5L EcoBoost - Various Warning Indicators/Lack Of Power - DTCs P0107, P0108 And/Or P0109 🎬 Watch: This video shows the TSB-specific repair for these codes.'. This bulletin supersedes TSB 19-2183 and confirms a faulty MAPT sensor as the cause. It applies to 2018-2019 Explorer, Flex, Taurus, and Lincoln MKT vehicles.
• TSB 19-2183: The original TSB identifying the faulty MAPT sensor as the cause for P0107, P0108, and/or P0109 on these vehicles. It provided the specific PID comparison diagnostic procedure.
• Bulletin #TSB-2212: This manufacturer bulletin notes that a faulty MAPT sensor may cause a wrench lamp, Service AdvanceTrac message, Hill Start Assist Not Available message, and/or lack of power when DTCs P0107, P0108, and/or P0109 are present.

Platform-Specific Known Issues

• Ford has issued TSB 19-2212 (superseding 19-2183) specifically for this issue on 2018-2019 Flex models with the 3.5L EcoBoost engine, confirming a faulty MAPT sensor as the root cause.
• Failure of this sensor often disables other vehicle systems that rely on accurate engine torque data, such as the AdvanceTrac stability control and Hill Start Assist, leading to multiple warning messages on the dashboard. This can be alarming but is a direct symptom of the sensor failure and is resolved upon its replacement.

Mechanic-Grade Diagnostic Values

• 5-Volt Reference Wire Voltage — expected: 4.8V to 5.2V DC with Key On, Engine Off (KOEO).. Failure: Voltage outside this range points to a problem with the PCM or the wiring, not the sensor itself.
• Ground Wire Voltage — expected: Less than 100 millivolts (0.1V).. Failure: A reading higher than 0.1V indicates a poor ground connection, which can cause incorrect sensor readings.
• Signal Wire Voltage (KOEO) — expected: Approximately 4.5V to 5.0V.. Failure: This high voltage reading is normal with the engine off, as the sensor is reading atmospheric pressure. A P0108 is set when the voltage remains this high after the engine starts.
• Signal Wire Voltage (Engine at Idle) — expected: Should drop to between 1.0V and 2.5V.. Failure: If the voltage stays high (near 4.5V) at idle, it confirms a 'Circuit High' condition, strongly indicating a faulty sensor that is not responding to engine vacuum.

Scan Tool Commands That Help

• Ford IDS (or equivalent professional scanner): Datalogger / Live Data Monitoring — This is not a command but the primary diagnostic function. It is used with the Key On, Engine Off to compare the MAP, BARO, TCBP, and TURBO INLET pressure PIDs simultaneously. This comparison is the specific diagnostic step called for in TSB 19-2212 to confirm a faulty sensor.
• Any OBD-II Scanner: Erase Codes — Used after the new MAPT sensor has been installed to clear the P0108 and any related codes from the PCM's memory. No special relearn or adaptation procedure is required for this repair.

Wiring & Ground Locations

• MAPT Sensor Connector Pin 1 (Typical) — On the sensor connector at the top of the intake manifold.. This pin is the 5-volt reference supplied by the PCM. A missing or incorrect voltage here indicates a wiring or PCM issue, not a sensor failure.
• MAPT Sensor Connector Pin 2 (Typical) — On the sensor connector at the top of the intake manifold.. This is the sensor ground circuit. High resistance or an open on this wire will cause the sensor's signal voltage to be skewed high, directly causing a P0108. It should read less than 0.1V.
• MAPT Sensor Connector Pin 3 (Typical) — On the sensor connector at the top of the intake manifold.. This is the signal return wire to the PCM. A P0108 code means this wire is carrying a voltage that is too high (stuck near 5V) when the engine is running. This can be caused by an internal sensor failure or a short to voltage in the harness.
• MAPT Sensor Connector Pin 4 (If equipped) — On the sensor connector at the top of the intake manifold.. On a 4-wire MAPT sensor, this pin is for the integrated Intake Air Temperature (IAT) sensor signal. A fault on this circuit would typically set a different code (e.g., P0113) but would not directly cause a P0108.

Real Owner Repair Stories

• YouTube video 'Ford 3.5L Ecoboost: P0107 P0108 P0109 - MAP Sensor Replacement' (2018-2019 Ford Explorer/Flex/Taurus or Lincoln MKT with 3.5L EcoBoost V6) — Sluggishness from a stop, lack of power, feeling like a transmission concern, and codes P0107, P0108, or P0109.
  ❌ Tried (didn't work) The video directly addresses the TSB, implying that other diagnostic paths are unnecessary.
  ✅ What actually fixed it Replacing the Manifold Absolute Pressure (MAP) sensor, part number AA5Z-9F479-E, located on top of the intake manifold. The repair involved removing one T20 Torx screw, disconnecting the connector, and swapping the sensor, which immediately resolved the issue after clearing the codes.

OEM Part Supersession History

• AA5Z-9F479-B → AA5Z-9F479-E (Motorcraft CX-2633) — Updated part revision from Ford to address the high failure rate documented in TSBs.
  Heads up: The 3.5L EcoBoost engine requires a 3-bar MAP sensor (like AA5Z-9F479-E) to read boost pressure. Using a sensor from a naturally aspirated 3.5L (e.g., Motorcraft CX2526 / DV2A-9F479-AC) will cause incorrect readings and performance issues, even if it physically fits.

Model Year Variations Within This Range

• 2018-2019: No significant variations related to this specific P0108 issue are documented within the 2018-2019 model years for the 3.5L EcoBoost. Both years are covered by the same TSB 19-2212 and use the same replacement part.

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. Explicitly cited in Ford TSB 19-2212 and 19-2183 as a companion code that frequently triggers alongside P0108 due to the same MAPT sensor failure.
• P0109 — Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent. Also explicitly cited in Ford TSB 19-2212 and 19-2183 as a companion code indicating the same MAPT sensor failure.
• P0112 — Intake Air Temperature Sensor 1 Circuit Low. Because the 3.5L EcoBoost uses a combined MAPT (Manifold Absolute Pressure and Temperature) sensor, internal failure of the unit can also trigger temperature-related circuit codes.
• P0113 — Intake Air Temperature Sensor 1 Circuit High. Related to P0108 because the temperature and pressure sensors share the same physical housing (MAPT sensor) and wiring harness.
• U0401 — Invalid Data Received From ECM/PCM. Often triggered in companion modules (like the ABS module) when the MAPT sensor fails, causing the 'Service AdvanceTrac' and 'Hill Start Assist Not Available' messages due to missing or invalid engine torque data.

Frequently Asked Questions