P0108 Code: Manifold Absolute Pressure/Barometric Pressure Circuit High Input

What the P0108 code means

The MAP sensor measures the pressure inside the intake manifold. With the engine running, that pressure is always below atmospheric, because the pistons draw in more air than the throttle lets through. It only approaches atmospheric at full load, and it only exceeds it on turbocharged or supercharged engines.

The P0108 code is set when the signal exceeds the expected maximum, typically more than 4.8 volts sustained. On a naturally aspirated engine that amounts to claiming there is no vacuum in the intake, which is impossible with the engine turning.

Compared with P0106, which flags a valid but inconsistent signal, this one points directly to an electrical fault or to a total loss of the connection with the manifold.

The three causes that explain it are the sensor hose disconnected or broken, so the sensor reads ambient air instead of vacuum, a signal wire shorted to a voltage line, and an open ground, which stops the internal circuit from pulling the voltage down even though the sensor is intact.

There is one scenario worth ruling out early because it has nothing to do with the sensor: the engine being off. With the key on and the engine off, the correct reading is atmospheric pressure, which shows up on the scan tool as a high value. If someone reads that as an anomaly without starting the engine, the diagnosis starts off crooked. This code only makes sense when evaluated with the engine turning.

Here is a quick test that separates the sensor from the rest of the circuit. With the engine at idle, briefly disconnect the sensor hose if it is mounted remotely. The reading should jump right up to atmospheric pressure and fall back when you reconnect it. If it does not move, the sensor is not measuring, and the problem is the sensor or its wiring.

P0108 code symptoms

• Check engine light on.
• Mixture too rich, with black smoke and a strong gas smell.
• Fuel use clearly higher.
• Rough idle, or an engine that stalls.
• Jerking and loss of power.
• Hard starting when hot.
• Possible limp mode.
• Pressure reading pinned at the maximum with the engine running.
• The reading does not change when the sensor hose is disconnected and reconnected.

Likely causes of the P0108 code

1. Sensor hose disconnected, broken or cracked on sensors mounted away from the manifold.
2. Signal wire shorted to a voltage line.
3. Sensor ground open or with high resistance.
4. MAP sensor failed internally.
5. Connector with moisture or conductive residue between pins.
6. Manifold pressure port clogged, which stops it from passing the vacuum.
7. Sensor gasket missing or misplaced.
8. Wiring rubbed against a power line.

How to diagnose the P0108 code step by step

1. Check the sensor hose if it is mounted remotely. If it is disconnected or broken, the sensor reads ambient air and the reading goes to the maximum.
2. Watch the reading with the engine running. At idle it should read between 25 and 40 kilopascals (about 7 to 12 inHg), and a value close to atmospheric confirms the fault.
3. Check the sensor ground. An open ground pushes the signal to the maximum with the sensor intact.
4. Unplug the sensor and watch the reading. If the high voltage persists, the problem is in the wiring.
5. Look for shorts between the signal wire and the power lines.
6. Check the manifold pressure port for a carbon clog.
7. Inspect the connector for moisture and conductive residue.
8. Verify the sensor gasket is present and seated.
9. Briefly disconnect and reconnect the hose with the engine at idle. The reading should rise to atmospheric and fall back, and if it does not move, the sensor is not measuring.

How to fix the P0108 code

• Reconnect or replace the sensor hose if it is loose, cracked or crushed.
• Repair the sensor ground down to bare metal, checking that its voltage drop is below 0.2 volts.
• Fix the short on the signal wire and protect the repaired section.
• Clean the manifold pressure port if it is clogged with carbon.
• Dry and clean the connector, and protect it with dielectric grease.
• Replace the sensor if the circuit is good and it still sends an impossible signal.
• Fit the sensor gasket correctly when you install it.

After the repair, check that the sensor reads atmospheric pressure with the key on and drops to the normal range with the engine at idle.

Replace the sensor if it does not react to disconnecting its hose with the engine running, once you have ruled out the wiring and the ground.

Technical reference data

• Typical signal: 0.5 to 4.5 volts. Above 4.8 volts sustained sets the code.
• Pressure at warm idle: between 25 and 40 kPa on a healthy naturally aspirated engine.
• Pressure with the key on and the engine off: atmospheric, about 101 kPa (14.7 psi) at sea level.
• An open ground pushes the signal to the maximum even if the sensor is intact.
• P0107 is the opposite code: voltage too low.
• Altitude lowers the atmospheric reference pressure.
• When you disconnect the hose with the engine at idle, the reading should rise to atmospheric pressure immediately.

Brand-specific notes

On sensors mounted away from the manifold, the hose is as suspect as the sensor itself and much cheaper. Check all of it before you buy anything, paying attention to hardened ends that crack when you take them off.

An open ground is the second cause that gets the most sensors replaced for no reason. Measure its voltage drop before you decide, because if it is high, the sensor is perfectly fine. Keep that in mind with any P0108 code.

Frequently asked questions about P0108