Fix P0108: Mechanic’s solutions that WORKED

The code P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input indicates that the vehicle’s computer has detected a higher than expected voltage from the Manifold Absolute Pressure (MAP) sensor, suggesting it is reading the air pressure within the intake manifold as abnormally high. This can be due to various reasons such as a faulty sensor, wiring issues, or a vacuum leak.

P0108 quick overview

Meaning	P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input
Is it serious?	It can be, as it may lead to poor engine performance, increased emissions, and poor fuel economy.
Possible causes	– Faulty MAP sensor – Electrical short or open in the MAP sensor circuit – Vacuum leak affecting the MAP sensor’s reading – Issues with the PCM, though this is less common
How to diagnose?	Check for additional codes to identify if there are related issues. Inspect the MAP sensor for physical damage or contamination. Examine wiring and connectors for corrosion, damage, or loose connections. Test sensor voltage to ensure it falls within the expected range. Consult TSBs for any known issues with the vehicle model. Perform a smoke test to find any vacuum leaks. Consider ambient temperature effects if the issue is intermittent and climate-related.

How to fix P0108 – learn from mechanics

I looked into P0108 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Jeep

Vehicle Information 2004 Jeep Grand Cherokee Laredo, 4.7L

Issue + Repair History

• Stalling when decelerating to a stop
• MIL (Malfunction Indicator Lamp) light on
• Aftermarket O2 sensor installed by owner
• Replaced split breather vacuum hose due to a large vacuum leak
• Codes: P0171 (lean), P0132 (O2 sensor voltage high), P0108 (MAP sensor voltage high), P1195 (O2 sensor slow switching)

Other OBD2 Codes + Test Results

• MAP sensor voltage would go to 5v instantly upon engine start, setting code P0108

What Are People Suggesting to Fix Issue

• Check MAP sensor voltage with KOEO (Key On Engine Off) and KOER (Key On Engine Running)
• Replace aftermarket O2 sensor with OE (Original Equipment) sensor if it is causing voltage issues

What Was the Final Fix

• Replaced faulty aftermarket B1S1 left upstream O2 sensor with an OE sensor to correct MAP sensor voltage issue

Case #2: Chrysler

Vehicle Information 2001 Chrysler Town & Country LXi, 3.8L

Issue + Repair History

• Sudden poor running condition and check engine light on
• Codes: P0107 (MAP Sensor Voltage Too Low), P0108 (MAP Sensor Voltage Too High), P0206 (Injector #6 Control Circuit), P1496 (5 Volt Supply Output Low)
• Found and repaired bare wires in engine wiring harness
• P0108 code persisted after repairs

Other OBD2 Codes + Test Results

• Fuel Pressure: 59 PSI

What Are People Suggesting to Fix Issue

• Check if MAP sensor voltage changes when driving or applying vacuum
• Expect approximately 1.3 volts on MAP sensor at idle
• Inspect main wire harness for damage, especially near the solenoid pack at the transaxle
• Review TSB for bracket to move wire harness away from transaxle

What Was the Final Fix

• Checked wiring harness from PCM to engine harness connector
• Replaced PCM and programmed it
• MAP sensor code still present, then replaced MAP sensor which resolved the code
• Believed that shorted wires spiked the PCM and backfire damaged the MAP sensor

Case #3: Subaru

Vehicle Information 2004 Subaru Impreza WRX STI, 2.5L

Issue

• Check Engine Light (CEL) on with OBD-II code P0108 indicating manifold pressure high.

Related Repair History

• Vehicle is stock with no modifications.
• No prior related repair history.

Initial Diagnostic Steps and Suggestions

• Given the car is relatively new, the repair could potentially be covered by warranty.
• Suggested to check the MAP sensor connection to ensure it is not disconnected.
• Consider that the wastegate might not be opening at low RPM due to a dirty or corroded diaphragm, bent linkage, or vacuum issue.
• Inspect for any loose vacuum hoses around the air filter and air duct.
• Check the vacuum connection between the manifold and MAP sensor for leaks.

Final Fix

• The problem was diagnosed as a faulty manifold pressure sensor, with part number 22627AA210 (Sensor Ay.T.R).
• The car was repaired under warranty.
• P0108 code has not returned since the repair.

Case #4: Pontiac

Vehicle Information 1997 Pontiac Sunfire GT, 2.4L engine

Issue + Repair History

• Hesitation and rough running in cold weather
• Intermittent problem, occurs after prolonged cold weather driving
• MIL on with OBD2 code P0108
• Previous repairs: MAP sensor replaced multiple times, PCM replaced and updated under recall
• Other OBD2 codes mentioned: P0171 (lean condition), P1171 (lean on acceleration)

What Are People Suggesting to Fix Issue

• Check MAP sensor hose for cracks that could cause false readings
• Replace oil pressure relief valve due to a TSB on high oil pressure causing valves to stay open
• Install a MAP sensor bleed T assembly into the vacuum line to prevent issue

What Was the Final Fix

• The problem has not reoccurred due to warmer weather
• Plan to reroute the MAP sensor vacuum line if the issue returns in cold weather
• No final fix applied yet due to the intermittent nature of the problem and customer’s decision to wait

Case #5: Ford

Vehicle Information 1997 Ford International 4700 with DT-466 engine, standard transmission

Issue + Repair History

• Truck dies intermittently
• Found DTCs for APP sensor and P0108 (BARO sensor code)
• APP sensor replaced after a glitch was found in waveform
• P0108 code persisted despite replacing the BARO sensor
• Ground and 5-volt reference OK, but no signal change under pressure or vacuum

What Are People Suggesting to Fix Issue

• Check and pin out the wiring from ECM to BARO sensor before considering ECM replacement

What Was the Final Fix

• After consulting on an HD/Fleet forum, determined the BARO sensor was shorted to ground
• Replacing the BARO sensor resolved the issue

Advice	Diagnostic Step Description
Double-check MAP/BARO sensor wiring	Inspect the wiring for shorts, disconnections, or corrosion to ensure sensor is receiving proper signals.
Inspect MAP/BARO sensor hose	Check for cracks or disconnections that could cause false readings due to vacuum leaks.
Consider temperature effects on the MAP sensor	Be aware that cold weather can cause issues such as freezing at the MAP sensor port.
Replace the MAP/BARO sensor if faulty	If diagnostics indicate the sensor is not functioning correctly, replace it.
Consult technical service bulletins (TSBs)	Look for manufacturer-issued TSBs that may address known issues with MAP/BARO sensors for specific models.