P0107 and P0108: MAP circuit low and high — hose, connector or sensor

The manifold absolute pressure sensor tells the ECU how much air is entering the engine, which determines how much fuel to inject. When its signal goes outside the plausible voltage window, you get P0107 (low) or P0108 (high).

The word “circuit” makes people reach for a multimeter. Reach for a torch first — on a large proportion of these, the fault is a hose.

Related: P0106 MAP sensor range/performance and MAF/MAP sensor diagnostics.

What each code means physically

Code	Signal	Typical cause
P0107	Voltage too low	Open circuit, ground short, sensor failure
P0108	Voltage too high	Lost vacuum supply, disconnected hose, short to power

P0108 is the more common of the pair, and its most frequent cause is not electrical at all. A sensor that sees no vacuum reads atmospheric pressure, which on many vehicles produces a high voltage the ECU rejects.

That happens when the hose falls off, splits, or fills with oil.

Check these in this order

1. The hose, if your sensor uses one

Some sensors mount directly on the manifold; others connect by a short rubber hose. Where a hose exists, it is the first thing to inspect.

Look for:

• A hose that has come off at either end.
• Splitting at the ends, where rubber hardens first.
• Oil or fuel inside the hose, which blocks the signal.
• Collapse under vacuum, which a hardened hose does readily.

This inspection costs nothing and resolves a meaningful share of P0108 cases.

2. The connector

Three pins on most sensors: 5 V reference, ground, signal. Check for corrosion, and check that the connector is fully latched — a partially seated connector is a classic intermittent.

3. The reference voltage

With ignition on, the reference pin should read close to 5 V. If it does not, the fault is upstream of the sensor. A shorted sensor can pull down the 5 V reference shared with other sensors, which is why P0107 sometimes arrives with a crowd of unrelated sensor codes.

If you have four sensor codes at once, suspect the shared reference rather than four sensors.

4. The sensor itself

Last. A sensor that reads a plausible value at key-on and does not change when the engine starts is dead — but you cannot conclude that until the hose and the reference are eliminated.

The key-on test that takes 30 seconds

With ignition on and engine not running, MAP should read approximately atmospheric pressure — around 100 kPa at sea level, lower at altitude.

Start the engine. At idle, manifold vacuum should pull it down substantially, typically into the 25–40 kPa range on a naturally aspirated petrol engine.

Reading	Interpretation
~100 kPa key on, drops at idle	Sensor working
~100 kPa and stays there at idle	No vacuum reaching sensor
Fixed at 0 or 255	Circuit fault, not a measurement
Wanders at steady idle	Failing sensor or unstable vacuum

That comparison is more useful than any single number, because it tests the sensor against a condition you already know the answer to.

Consequences while it is faulty

A bad MAP signal is a bad fuelling calculation, so expect some combination of:

• Rough or unstable idle: fluctuating idle RPM causes.
• Hesitation under load.
• Black smoke or heavy fuel consumption if the ECU is fooled into over-fuelling.
• Hard starting.
• Limp mode on vehicles that treat it as critical.

The ECU may substitute a calculated value from throttle position and RPM, which is why some cars drive almost normally with the code stored. That is a fallback, not a fix.

On turbocharged engines

Boost pressure sensors work the same way, and the same hose logic applies — but on a turbo engine a MAP fault and a boost leak produce overlapping symptoms.

Check the sensor before chasing boost pipework, and check boost pipework before condemning a turbocharger: turbocharger boost leak diagnostics.

Before you buy the part

1. Inspect the hose and its ends.
2. Unplug and inspect the connector for corrosion and oil.
3. Check for other sensor codes — a crowd means a shared reference.
4. Do the key-on versus idle comparison.
5. Only then order a sensor.

The practical next step: pair an ELM327 adapter, open the free tier of the app and watch MAP go from atmospheric at key-on to vacuum at idle. If it never moves, you have found the fault without a single tool.