P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input
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What does the P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input mean?
DTC P0108 is defined as “Manifold Absolute Pressure/Barometric Pressure Circuit High Input.” In plain terms, the ECM has detected a MAP sensor signal voltage that is above its normal range for given engine conditions.
The MAP sensor monitors the intake manifold’s absolute pressure (engine vacuum). Under load (throttle open, higher RPM) manifold pressure rises; at idle, manifold vacuum is high and pressure low. The ECU uses this MAP data to gauge engine load and adjust air-fuel ratio, ignition timing and EGR operation.
A separate BARO sensor measures ambient atmospheric pressure. In practice, many modern vehicles integrate MAP and BARO in one unit or use the MAP sensor’s key-on reading as the barometric reference. The only difference is location – the MAP sensor is plumbed to the manifold, while a BARO is vented to outside air.
The ECM monitors the MAP/BARO signal as part of its engine load calculation. In speed-density fuel injection systems, the ECM combines the MAP voltage with inputs like engine speed (RPM) and throttle position (TPS) to estimate airflow and set fuel and ignition.
P0108 means the ECM sees an abnormally high MAP sensor signal voltage. The sensor output is typically stuck near 4.5–5.0 volts when engine conditions do not justify such a high reading. Unlike P0106, which indicates a performance or plausibility problem, P0108 is usually caused by a high-voltage circuit fault, a failed MAP sensor, a disconnected vacuum hose, or a signal wire shorted to the 5V reference circuit.
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When the P0108 Triggers?
The Engine Control Module (ECM) continuously monitors the Manifold Absolute Pressure (MAP) sensor signal to determine engine load and calculate the correct fuel injection and ignition timing. To ensure the MAP sensor is operating correctly, the ECM performs several plausibility checks by comparing the MAP signal against engine operating conditions such as throttle position, engine speed, and barometric pressure.
The MAP sensor typically receives a 5-volt reference signal and ground from the ECM and returns a voltage signal that changes according to intake manifold pressure.
Typical MAP Sensor Voltage Readings
| Condition | Typical MAP Output Voltage | Notes |
|---|---|---|
| Key ON, Engine OFF (KOEO) | ~4.5–5.0 V | Sensor sees ambient pressure; should match baro |
| Idle (High vacuum) | ~0.8–2.0 V | Expect low voltage; high reading (e.g. >4 V) is abnormal |
| Light Cruise (Moderate vacuum) | ~2.0–3.5 V | Proportional to pressure |
| Wide Open Throttle | ~4.5–5.0 V | Near 5 V with throttle fully open |
| P0108 Fault Threshold | ≈4.3–4.5 V (sustained) | Code sets if exceeded for a few seconds |
Note: Actual values vary depending on vehicle manufacturer, altitude, engine design, and sensor calibration.
For example, a 2006 Honda Insight sets P0108 when the MAP voltage is ≥4.49 V for over 2 seconds. (In many vehicles the trip point is roughly 4.3–4.5 V.)
In summary, P0108 triggers when the MAP/BARO sensor output voltage stays high (typically <4.5–5.0 V) for more than a brief time.
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When Is P0108 Set (Trigger Conditions)?
- Throttle Wide Open / Key-On: Normally, with ignition ON (engine off) or at wide-open throttle, manifold pressure equals atmospheric (~0 PSI vacuum) so the MAP output is high (near 4.5–5.0 V). This is expected. However, P0108 will set if even higher voltage is seen or if high voltage occurs under conditions not allowing full throttle.
- Idle/High Vacuum: At idle or closed throttle, manifold vacuum is high, so MAP voltage should be low (~0.8–2.0 V for most NA engines). Under these conditions, a high MAP voltage (e.g. >4 V) is abnormal and will set P0108.
- Fault Conditions: P0108 is typically flagged when the MAP signal is above its calibrated range. Manufacturer criteria vary, but e.g. GM’s PCM flags P0108 if MAP >4.3 V for ~3 seconds. Honda’s specification is MAP ≥4.49 V for 2+ seconds. In practice, if the sensor output stays pinned near 5 V or spikes above ~4.5 V during operation, the code should appear.
- Rationality Check: The ECM also compares MAP to other inputs (e.g. throttle position, RPM). If MAP voltage suggests “full manifold pressure” but throttle is closed, a disconnect/leak or sensor issue may be implied.
How to Prevent OBD Trouble Codes and Avoid the Check Engine Light
Regular vehicle maintenance is the best way to prevent OBD trouble codes and keep the check engine light from appearing. Follow your vehicle’s recommended service schedule, change engine oil and filters on time, use the correct fuel and fluids, and fix small problems before they turn into expensive repairs.
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How To Fix P0108?
Diagnosing P0108 follows a systematic approach:
| Steps | Action | Expected Result |
|---|---|---|
| 1 | Clear codes and road test | Confirm P0108 returns. Record current MAP voltage at idle and WOT. |
| 2 | Visual inspection | Vacuum hose connected and undamaged. No obvious sensor damage or oil/debris. |
| 3 | Inspect MAP sensor & connector | No corrosion, broken pins, or loose terminal on sensor plug. |
| 4 | Verify 5 V reference | With ignition ON, backprobe MAP’s 5 V supply wire: ~4.5–5.1 V. |
| 5 | Verify ground | Check MAP sensor ground: voltage drop should be near 0 V. |
| 6 | Check MAP signal KOEO | Key ON, engine OFF: MAP output ≈4.5–5.0 V (ambient). |
| 7 | Check MAP signal at idle | With engine idling: MAP ≈0.5–2.0 V (high vacuum). |
| 8 | Test sensor with vacuum pump | Apply vacuum: voltage should drop smoothly (e.g. ~3–4 V at ~5 inHg, ~1 V at ~20 inHg). |
| 9 | Analyze results | If MAP output stays near 5 V or does not respond: suspect a short in signal circuit or a bad sensor. If output changes normally: look for intermittent faults or incorrect code trigger. |
| 10 | Repair confirmed fault | Replace MAP sensor if faulty. Repair/replace wiring or connectors for any open/short. Fix intake leaks if found. |
| 11 | Clear codes & retest | Verify P0108 does not reappear and engine performance is restored. |
Diagnosing P0108 logical flowchart:
Read our free complete guide on Kindle and learn how to diagnose sensor-related issues with clarity and confidence.
STOP GUESSING. START DIAGNOSING. SAVE HUNDREDS ON REPAIRS.
Tired of expensive repair bills and mechanics who “parts-cannon” your car without finding the real issue? The “Check Engine” light shouldn’t be a mystery. This guide puts professional-level diagnostics in your hands.
Possible Root Causes of P0108
Some common root causes of the P0108 error code include:
1. Vacuum Leak (Intake or Hose Leak)
A vacuum leak (from a cracked hose, loose fitting, or intake manifold gasket leak) lets outside air into the manifold, causing the MAP reading to be lower (higher vacuum) than expected.
For example, a leak in the MAP hose or at the manifold boot means the sensor sees less pressure than the engine actually has. The ECU, comparing this aberrant low pressure to the expected value, will flag a fault.
Fix: Carefully inspect the intake system for vacuum leaks. Check all vacuum hoses, intake ducting, PCV lines, and intake manifold gaskets for cracks, loose connections, or damage. A professional smoke machine can be used to introduce non-toxic smoke into the intake system. Smoke escaping from hoses, gaskets, or fittings will help pinpoint the source of the leak. Once identified, repair or replace the faulty component and clear the trouble code.
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2. Faulty MAP Sensor
The MAP sensor itself may be defective (stuck diaphragm, internal short, or contamination). For example, the internal sensing element can wear out or be damaged by heat/oil. A faulty MAP often reports a fixed voltage (e.g. high or low) regardless of actual pressure.
Fix: Replace the MAP sensor with an OEM-quality unit. Many MAP sensors come with a pigtail harness; be sure to match the OE part number.
Recommended product: Bosch or Delphi MAP sensor
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3. Wiring/Connector Issue
Damaged wiring or connectors can cause intermittent or incorrect signals. Corrosion at the connector, a broken wire in the loom, or a short between the signal and 5V reference will all generate wrong voltage to the ECU.
Fix: Inspect the MAP sensor connector for bent pins, corrosion, or moisture. Wiggle the wiring harness while monitoring MAP voltage – spikes or drops indicate a wiring fault. Repair any chafed wires or replace the connector. Use dielectric grease on the connector to prevent corrosion.
Recommended product: A repair wire harness pigtail for your MAP sensor (if available), or general electrical repair kit (for splicing and insulating wires).
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4. Clogged/Dirty MAP Port
Carbon, oil, or debris in the MAP sensor’s vacuum port or hose can impede the pressure signal. For example, if the small hose fitting to the sensor is partially blocked, the ECU will read incorrect pressure.
Fix: Remove the MAP sensor and blow through its port and hose. Clean with a dedicated sensor or throttle-body cleaner (do not use harsh chemicals that leave residue). Ensure the port under the sensor is free of gasket material. If contamination has entered the sensor, replacement is safer.
Recommended product: Mass Airflow/MAP sensor cleaner (such as CRC or WD-40 LOD) to clean orifices without damaging the sensor.
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5. Faulty BARO Sensor (if separate)
Some engines have a separate barometric (BARO) pressure sensor. If the BARO sensor fails or its vent line is blocked, the ECU gets bad ambient pressure data. This usually only matters on cars where MAP and BARO are distinct.
Fix: If your vehicle has a separate BARO (often on the intake plenum or MAF housing), test it like a MAP sensor (see service manual). A bad BARO can often set P0106/P0107/P0108 as well, but in some systems it may trigger P0106. Replace the BARO sensor if it’s defective.
Recommended product: Genuine BARO sensor or intake-manifold pressure sensor (often the same part number as MAP on some models).
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6. Faulty ECU (Rare)
In very rare cases, the powertrain control module itself is at fault (bad analog input for MAP/BARO). This could happen if the ECU’s internal reference source or ADC channel is damaged.
Fix: Confirm all else is good before blaming the ECU. If wiring and sensors test fine, an ECU reflash or replacement may be needed. This is usually done at a dealership or professional shop.
Note: Always double-check wiring, grounds and sensors first – ECM failure is uncommon.
Common Diagnostic Mistakes
- Skipping 5 V/Ground Checks: A frequent error is swapping the MAP sensor without verifying the 5 V reference or ground. Always confirm the sensor is receiving proper power and ground before condemning it.
- Ignoring Wiring: Don’t assume a new sensor will fix it. A short to 5 V (for example from damaged insulation) will force the output high even with a good sensor. Always inspect wiring continuity and condition.
- Misreading Normal High Throttle: Remember that MAP approaches 5 V at full throttle. However, if P0108 sets in idle or during cruise (not full WOT), that indicates a true fault. In normal WOT conditions the code often won’t be set if the system logic expects it.
- Overlooking Vacuum Issues: While P0108 is mostly electrical, a severe vacuum leak or disconnected hose can drive manifold pressure high. It’s easy to default to “it must be electrical,” but a broken vacuum line could be the root cause.
- Not Using Live Data: Sometimes freeze-frame data isn’t clear. Using a scan tool to observe the MAP reading at idle vs. accelerating can quickly reveal an issue. A MAP voltage that doesn’t change with throttle is a red flag.
Related Codes
- P0105: MAP/BARO Circuit Malfunction: Indicates a reference voltage or circuit problem (open/short) in the MAP sensor circuit. Often P0105 must be resolved before addressing P0108.
- P0106: MAP/BARO Circuit Range/Performance Problem (sensor out of normal range)
- P0107: “MAP/BARO Circuit High” – The MAP voltage is too low (below expected).
- P0171 / P0174: “System Too Lean (Bank 1/2)” – Lean fuel trim codes. A vacuum leak (a common P0108 cause) or failing MAP can cause these lean codes.
- P0300 (and P0301–P0308): “Random/Multiple Cylinder Misfire” – Erratic MAP signals or vacuum leaks can lead to misfires under load, setting P0300 series faults.
- P0110: “Intake Air Temperature Sensor” – While not directly a MAP code, it’s related in that it measures intake conditions. It’s worth checking IAT if the intake is contaminated.
| Code | Definition | What It Means |
|---|---|---|
| P0105 | MAP/BARO Circuit Malfunction | General electrical fault in the MAP/BARO circuit. ECM cannot trust the sensor signal. |
| P0106 | MAP/BARO Circuit Range/Performance Problem | Sensor signal exists but doesn’t match expected engine operating conditions. |
| P0107 | MAP/BARO Circuit Low Input | MAP voltage stuck too low (typically below ~0.5V). Often caused by a short to ground, faulty sensor, or wiring issue. |
| P0108 | MAP/BARO Circuit High Input | MAP voltage stuck too high (typically above ~4.5V). Often caused by a short to 5V, failed sensor, or disconnected vacuum source. |
| P0109 | MAP/BARO Circuit Intermittent | Signal drops in and out unexpectedly due to loose connections, damaged wiring, or intermittent sensor failure. |
What causes code P0108?
P0108 is most often caused by an electrical fault in the MAP sensor circuit. Common culprits are a bad MAP sensor (internally shorted or stuck), a short in the signal wire to the 5 V reference, or an open circuit. If the MAP signal remains too high (near 5 V) for too long, the ECM sets P0108. Less commonly, a large vacuum leak (or disconnected hose) can reduce manifold vacuum so much that the MAP reads “high” and triggers the code. A faulty ECM reference/regulator is rare but possible.
How do I diagnose P0108?
Start by scanning and clearing the code, then reproducing it. Check the MAP sensor’s output voltage with a multimeter or scan tool. With the key ON engine-off, it should be ~4.5–5.0 V. At idle it should drop to ~0.5–2.0 V. If the output is abnormally high or doesn’t change with vacuum, backprobe the connector: verify the 5 V reference and ground are good. Use a handheld vacuum pump to see if the voltage falls smoothly as vacuum increases. In summary: inspect wiring, test reference and ground, and verify the sensor’s response to vacuum.
Can a vacuum leak cause P0108?
Yes. A significant vacuum leak (or disconnected MAP hose) will cause the intake manifold pressure to rise (vacuum drops), forcing the MAP sensor output toward its maximum. The ECM will see this as an unexpectedly high pressure signal and set P0108. In practice, vacuum leaks more often trigger P0107 (low input) or performance codes, but they are listed as possible causes of P0108.
What is the difference between P0107 and P0108?
Both involve the MAP sensor circuit, but P0107 is a low input code (the sensor reads too low, usually below ~0.5 V), while P0108 is a high input code (sensor reads too high, usually above ~4.5 V). In other words, P0107 means “signal is lower than expected” and P0108 means “signal is higher than expected.” They often have similar causes (sensor or wiring faults) but opposite symptoms.
What are the symptoms of P0108?
The check engine light will be on. Other symptoms can include rough or unstable idle, poor throttle response, hesitation or stalling, and reduced fuel efficiency. In some cases, the vehicle may enter limp mode or struggle to start. However, symptoms can overlap with other issues, so use live data to confirm a MAP anomaly.
Can I drive with a P0108 code?
Technically the engine may run with the code stored, but it’s not recommended to continue driving without diagnosis. A faulty MAP reading can cause rich/lean conditions, causing poor performance or even engine damage over time. It’s safest to fix P0108 promptly to restore proper engine management.
How much does it cost to fix P0108?
If the problem is just a bad sensor, a MAP sensor replacement (parts + labor) might cost $80–$200 depending on vehicle. If wiring or ECU repairs are needed, labor could be higher. Using a scan tool and meter for diagnosis can avoid unnecessary parts replacement.
How can I test the MAP sensor myself?
With the engine running, use a DMM on the MAP signal wire. At idle it should be around 0.5–2 V and climb to ~4.5–5.0 V by wide-open throttle. Also check the sensor’s 5 V supply (key ON) and ground. A handheld vacuum pump can be used: apply vacuum and confirm the voltage drops smoothly. If the sensor doesn’t change output or reads stuck-high, it’s faulty.
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