Fuel Delivery
P0108
Manifold Absolute Pressure Circuit High Input
P0108 applies to Manifold Pressure / Engine Load Sensing and indicates MAP circuit high input.\n\nThe PCM monitors MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure. Electrical, connector, shared-circuit and real mechanical…
Diagnostic Snapshot
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Before diagnosing this code, it helps to understand the system behind it.
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P0108 identifies MAP circuit high input involving manifold absolute pressure (MAP) sensor signal circuit. The PCM evaluates MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure.
Diagnose the wording of the fault, not the component name alone. Compare map at key-on/engine-off and idle, then determine whether the high reading is electrically false or mechanically real. Use OEM specifications for circuit values and monitor thresholds.
Risk: Moderate to High if the PCM calculates excessive load. Engine/catalyst risk: Low to Moderate. Verify the repair by reproducing the original conditions and confirming the monitor completes without a pending or current code.
What You'll Learn
- Exact meaning of P0108
- Best freeze-frame and live-data clues
- Circuit versus mechanical test direction
- Repair verification
Think Like a Technician
Treat P0108 as evidence, not a parts order. Decide whether MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure is electrically wrong or accurately reporting a mechanical condition, then prove that path with an independent test.
What This Code Means
P0108 means the PCM judged MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure to be outside the calibrated expectation.
The exact fault is MAP circuit high input; it does not automatically prove manifold absolute pressure (MAP) sensor signal circuit has failed.
System Overview
Manifold Pressure / Engine Load Sensing provides the PCM with an input or controlled response used for engine operation and emissions.\n\nDiagnosis should follow the chain of command/input, circuit integrity, physical response and feedback so an electrical defect is not confused with a real mechanical condition.
Why This Code Sets
The monitor runs only when calibration-specific prerequisites such as usable related signals, suitable operating conditions and stable voltage are met.
When enabled, the PCM evaluates MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure. If the result remains outside its calibrated window long enough, P0108 is stored. Use exact OEM thresholds rather than universal values.
Common Symptoms
- Check Engine Light
- Possible failed emissions inspection
- Driveability symptoms depend on how strongly the fault changes load, timing, temperature or throttle control
- Possible reduced power, roughness, hesitation, hard starting or fuel-economy change depending on the system
- Fail-safe strategy may substitute a default value or disable an actuator
Most Likely Causes
- 1. MAP sensor connector/wiring fault or poor terminal contact
- 2. Blocked, contaminated, cracked, pinched, or disconnected MAP sensing port/hose where used
- 3. Sensor reference/supply or ground circuit problem
- 4. Biased or failed MAP sensor
- 5. Vacuum leak or throttle/intake condition causing genuinely abnormal manifold pressure
- 6. Incorrect valve timing, low compression, EGR flow, exhaust restriction, or boost-control fault creating a real pressure plausibility problem
- 7. PCM calibration or input rationality issue after primary causes are eliminated
Freeze Frame Clues
- RPM/load and vehicle speed at failure
- System voltage
- ECT/IAT and time since start
- Relevant Manifold Pressure / Engine Load Sensing command/feedback PIDs
- Throttle/load or fuel-trim context when applicable
- Companion codes that may share a root cause
Live Data Expectations
Graph MAP with BARO, throttle position, RPM and calculated load. Key-on/engine-off MAP should be logically consistent with atmospheric pressure for the design; after start-up on a naturally aspirated gasoline engine it should reflect manifold vacuum and then move promptly toward atmospheric pressure as the throttle opens. If the electrical signal moves smoothly but manifold pressure itself is abnormal, test the engine/intake system rather than condemning the sensor.
Typical Verification Tests
- Confirm P0108 is absent from current and pending memory
- Recreate the freeze-frame operating range
- Graph key Manifold Pressure / Engine Load Sensing data for smooth/plausible response
- Repeat wiggle/heat test if originally intermittent
- Complete required relearn
- Run the applicable readiness monitor
Before You Condemn
- Confirm exact code definition/component identity
- Save freeze-frame
- Verify voltage and grounds
- Inspect connector/terminal fit
- Compare scan data with physical reality
- Perform OEM circuit/functional test
- Rule out mechanical causes
- Document the failed test before replacement
Before Replacing Parts
Save freeze-frame, verify the exact component/pinout, inspect wiring and perform the simplest physical checks first. Compare map at key-on/engine-off and idle, then determine whether the high reading is electrically false or mechanically real. Replace a part only after its signal, circuit, response or OEM test proves it defective.
Diagnostic Workflow
- Confirm P0108 with a capable scan tool and record whether it is current, pending, history, or intermittent. Do not clear it yet.
- Save freeze-frame data and all companion codes. Note engine speed, load, coolant temperature, intake temperature, throttle position, system voltage, and the PIDs directly related to Manifold Pressure / Engine Load Sensing.
- Check technical service information for the exact year, engine, calibration, connector pinout, monitor prerequisites, and any known software or harness issues. Do not substitute a generic pinout.
- Perform a focused visual inspection of manifold absolute pressure (MAP) sensor signal circuit, its connector, nearby harness routing, grounds, and any hoses or passages that affect the measurement or actuator.
- Verify battery and charging-system voltage are stable. Low system voltage can distort actuator operation and sensor diagnostics and can create misleading secondary codes.
- Compare map at key-on/engine-off and idle, then determine whether the high reading is electrically false or mechanically real.
- With key on and engine off, compare MAP to BARO or local atmospheric pressure as represented by the vehicle's available PIDs. They should be logically close on a naturally aspirated engine, subject to sensor strategy and altitude.
- Start the engine and observe the MAP change at idle. Determine whether the reading reflects real manifold pressure or an electrically biased signal.
- Inspect the MAP port, hose or manifold passage for carbon, oil, moisture, pinching or blockage. Verify the sensor is actually exposed to manifold pressure.
- Test reference/supply, sensor ground and signal according to the OEM circuit design. Do not assume every MAP sensor uses the same voltage range.
- Apply a controlled vacuum/pressure source to a removable sensor when the service procedure permits and compare scan/meter response for smoothness and repeatability.
- If the electrical signal is valid but pressure is implausible, check for intake vacuum leaks, EGR flow, incorrect valve timing, low compression, exhaust restriction or boost-control faults as applicable.
- Compare MAP response to throttle position and engine speed during a snap-throttle or controlled road test. The signal should change promptly rather than remain fixed or jump erratically.
- Repair the verified circuit, sensor, vacuum passage or mechanical cause. Clear the code and any learned values only when service information calls for it.
- Re-run the monitor and confirm P0108 remains absent while MAP/BARO/load data respond plausibly across the operating range.
Labor & Inspection Checklist
- Verify VIN/engine and service information
- Scan all related codes and save freeze-frame
- Inspect manifold absolute pressure (MAP) sensor signal circuit connector/harness
- Check relevant fluid/intake/cooling/mechanical basics
- Test power/ground/reference/signal or actuator circuit
- Compare live data with an independent physical check
- Repair/relearn
- Verify monitor completion
Common Repairs
- Repair proven wiring/connector/power/ground fault
- Replace manifold absolute pressure (MAP) sensor signal circuit only after testing proves internal failure
- Correct verified mechanical/fluid/intake/cooling/timing cause
- Perform required relearn and monitor verification
Common Parts
- MAP sensor
- Connector pigtail
- Harness repair materials
- Vacuum/intake leak repair parts
Shop Notes
Document the PID/circuit result that proves the cause of P0108.
If the fault is intermittent, save a graph during a wiggle/road test. After repair, check pending codes and monitor completion.
Technician Notes
For P0108, focus on MAP signal or calculated pressure exceeding the expected range, especially when engine operating conditions should create lower manifold pressure.\n\nUse loaded circuit testing where appropriate and compare scan data with physical reality. Preserve pre-repair data for verification.
Mechanic's Tip
For P0108, put the most diagnostic PIDs on one graph instead of reading them one at a time. A synchronized graph makes it easier to see whether the PCM command changes first, whether the physical system follows, and whether the feedback signal is late, biased, noisy or simply reporting a real mechanical problem.
Common Mistakes
- Replacing manifold absolute pressure (MAP) sensor signal circuit from the code name alone
- Clearing freeze-frame before diagnosis
- Using universal specs instead of OEM data
- Skipping loaded circuit or physical verification
- Ignoring companion codes
- Failing to verify a pending-code-free drive cycle
Tools Used During Diagnosis
- Enhanced/graphing scan tool
- Digital multimeter
- OEM wiring diagram and service information
- Backprobe leads/terminal test tools
- Battery/charging-system tester
- Hand vacuum/pressure pump when sensor design permits
- Vacuum/pressure gauge
- Smoke machine
Manufacturer Notes
This is a generic OBD-II code. MAF and MAP system architecture varies considerably: some vehicles use frequency-output sensors, some use voltage signals, some integrate IAT with the MAF, and some use modeled airflow as a cross-check. Use the OEM wiring diagram and PID definitions before applying voltage or grams-per-second assumptions.
Customer Explanation
Your vehicle stored P0108, which means the computer found MAP circuit high input in the Manifold Pressure / Engine Load Sensing system. The code does not automatically mean manifold absolute pressure (MAP) sensor signal circuit must be replaced. Wiring, connectors, operating conditions and mechanical problems can create the same code. The correct repair starts by saving the fault data, checking the simple causes, and testing the system under the conditions that caused the warning light.
Frequently Asked Questions
What does P0108 mean?
P0108 means the PCM has identified MAP circuit high input involving manifold absolute pressure (MAP) sensor signal circuit. It identifies the monitored fault, not automatically a failed part.
Can I drive with P0108?
Usually suitable only for limited driving when the engine runs normally and no severe warning signs are present. Diagnose promptly.
What should I check first for P0108?
Compare map at key-on/engine-off and idle, then determine whether the high reading is electrically false or mechanically real. Save freeze-frame and related codes before clearing anything.
Does P0108 mean the sensor or actuator is bad?
No. Wiring, connectors, power/ground, mechanical conditions, contamination, shared circuits, calibration and the monitored component itself all have to be considered.
Will P0108 fail an emissions inspection?
Usually yes when the malfunction indicator lamp is commanded on, and clearing the code shortly before inspection can leave readiness monitors incomplete.
Can low battery voltage cause or complicate P0108?
Yes. Low cranking or charging voltage can affect sensor references, actuator response and module diagnostics. Verify electrical system health when voltage in freeze-frame is suspicious.
Should I clear P0108 before diagnosing it?
No. Record freeze-frame, pending codes and companion DTCs first. Clearing memory can erase the conditions that make the fault easier to reproduce.
When is professional equipment justified for P0108?
A bidirectional scan tool, oscilloscope, smoke machine, pressure/vacuum test equipment or OEM service information is justified when basic visual and circuit checks do not clearly prove the fault.
Can P0108 be intermittent?
Yes. Connector fretting, heat-related electronics, harness movement and marginal mechanical control can create faults that disappear in the bay. Graphing data during a road test is often more revealing than a static check.
How do I know the repair is finished?
Reproduce the original operating conditions, confirm the affected live data behaves normally, run the applicable monitor and make sure P0108 does not return as current or pending.
Related Atlas Resources
Review the related system chapter and OEM service information before specification-level testing.
Diagnostic Confidence
High after the code is reproduced and circuit/physical response is verified; Medium when the fault is intermittent and cannot be reproduced
Explore Related Atlas Resources
Related Diagnostic Codes
- P0112 — Intake Air Temperature Sensor Low Input
- P0113 — Intake Air Temperature Sensor High Input
- P0171 — System Too Lean (Bank 1)
- P0174 — System Too Lean (Bank 2)
- P0300 — Random/Multiple Cylinder Misfire Detected
- P0420 — Catalyst System Efficiency Below Threshold Bank 1
- P0107 — Manifold Absolute Pressure Circuit Low Input
- P0106 — Manifold Absolute Pressure Circuit Range/Performance
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