P0108 Code on a Buick: MAP Sensor Circuit High Voltage (Buick Guide)

P0108 on a Buick is "Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage." The MAP sensor's signal went close to its 5-volt ceiling and stayed there — higher than any real manifold pressure should produce. That makes it an electrical code, and the most common reason a signal reads high is not a failed sensor but a lost ground or an open in the sensor circuit. It is one of the few air codes that every era of Buick can set, from the 3800 V6 LeSabre and Park Avenue to the Encore GX turbo, and we found no GM bulletin naming it on any Buick — so diagnosis is pure circuit testing, done in the right order.

What Does P0108 Mean on a Buick?

The MAP sensor is a three-wire pressure transducer: a 5-volt reference from the ECM, a low reference (ground) back to the ECM, and a signal wire. Its output voltage rises as manifold pressure rises. At idle on a naturally aspirated Buick the signal is low because the manifold is under vacuum; at wide-open throttle it approaches atmospheric pressure; on a turbo Buick it keeps climbing under boost.

GM's wording is MAP Sensor Circuit High Voltage. GM's 2006 diagnostic parameters for the 3.8L V6 describe it as detecting a "continuous short to high in either the signal circuit or the MAP sensor." The 2021 tables that cover the Encore GX engines describe a "continuous short to power or open circuit" in the MAP signal circuit.

So P0108 is a circuit test. It says nothing about whether the engine has a vacuum leak — that would be P0106, the performance code.

Why a "High" Reading Usually Means an Open

People often assume "circuit high" means a wire shorted to battery voltage. That happens, but it is not the usual Buick fault. Think about how the circuit behaves when something lets go:

That is why the first electrical check is the low reference, and why a new sensor on a car with a broken ground wire fixes nothing.

Connectors matter as much as wires. The MAP sensor sits on top of the intake manifold on most Buicks, where heat cycles and engine movement work on the terminals for years. A connector whose lock tab broke during an earlier repair, or a terminal spread by a test probe, can lose its ground intermittently — often first in cold weather or over bumps.

The 5-volt reference on most Buick ECMs is shared with other sensors. If the reference shorts, several sensors drop out at once and you will see a cluster of "low" codes plus a 5-volt reference code such as P0641 or P0651. A lone P0108 points at the MAP sensor's own circuit.

Which Buicks Set P0108

Any Buick with a MAP sensor can set P0108. GM's published parameter tables list it for:

• 3800 V6 Buicks (L36, L67, L26, L32) — Regal, Park Avenue, LeSabre-era cars, LaCrosse, Allure and Lucerne. GM's 1997–2006 tables for the 3.8L list P0108.
• The Ecotec four-cylinders and 3.6L V6s in the LaCrosse, Regal, Verano, Enclave and Envision, in GM's 2015 and 2017 tables.
• Turbo Buicks — Encore 1.4T, Regal and Verano 2.0T, Envision 2.0T, Encore GX and Envista — where the MAP sensor reads well above atmospheric under boost.

One exception is worth knowing: GM's 2006 table for the 3.6L LY7 in the LaCrosse, Allure and Rendezvous of that era lists no MAP circuit codes at all. If a scanner shows P0108 on one of those, double-check the code and the engine before chasing a sensor.

We found no GM bulletin — TSB, preliminary information or special coverage — that names P0108 on a Buick. That is consistent with how circuit codes usually behave: a wiring fault is specific to the car in front of you, not a design pattern.

GM's Set Conditions

Two things follow. First, the turbo-engine sensor is ranged far above atmospheric pressure, so a reading equal to 390 kPa is impossible in normal running — it can only be electrical. Second, both versions are two-trip codes: the fault must be seen on two separate drives before the light comes on, so an intermittent connection can come and go for a while first.

The 3800 table also delays the test after a cold start by an amount that depends on coolant temperature — over a second at 30 °C and up to two minutes at −30 °C.

Symptoms of P0108

• Check engine light
• Rough running or hesitation as the ECM falls back on a default MAP value
• Rich running or poor fuel economy in some cases
• Hard starting or stalling in some cases
• Reduced power on some turbo Buicks
• Symptoms that come and go over bumps if a connector is loose

Causes and How to Confirm Each

How Is P0108 Diagnosed?

1. Read all codes. A lone P0108 points at the MAP circuit; several "low" codes plus a 5-volt reference code point at a shared reference.
2. Check MAP with key on, engine off. It should read close to barometric pressure. A reading pinned near the top of the range confirms the fault is present now.
3. Unplug the sensor and watch the reading. How it changes tells you whether the signal wire is shorted high or the sensor is pulling it up.
4. Test the low reference to ground at the connector.
5. Measure the 5-volt reference at the connector.
6. Inspect and pin-test the connector and the harness back to the ECM.
7. Replace the sensor only after the circuit tests good.
8. Clear and drive twice. It is a two-trip code, so one quiet drive does not prove the repair.

Parts and Cost

MAP sensors differ by engine — naturally aspirated and turbo sensors have different ranges, and turbo Buicks also have a separate boost sensor. Order by VIN.

GM Documents for P0108 on Buicks

No GM bulletin we found names P0108 on a Buick. These GM documents define the code for Buick engines:

Have a dealer check your VIN against current bulletins and campaigns rather than relying on any article, including this one.

What Other P0108 Pages Get Wrong

• "Replace the MAP sensor." A high reading most often comes from an open ground or connector. Test the circuit first.
• Blaming a vacuum leak. A leak changes manifold pressure within the sensor's normal range and sets P0106 or fuel trim codes — not a circuit-high code.
• Mixing up the MAP and boost sensors on turbo Buicks. They are separate parts with separate codes.
• Forgetting it is two-trip. A repair is not proven until the car has done two drives without the code.
• Listing it for every Buick engine. GM's 2006 table for the 3.6L LY7 shows no MAP circuit codes.

For how MAP, MAF and oxygen sensor faults differ, see GM MAF vs MAP vs O2 sensor: which to replace.

Frequently Asked Questions

Is P0108 serious?

It is not usually dangerous, but the engine is running on a substitute value and may run rich, hesitate or stall. Fix it soon to protect the catalytic converter and fuel economy.

Can a bad ground cause P0108?

Yes — it is one of the most common causes. With an open low reference, the sensor output floats up toward its 5-volt supply and the ECM sees "circuit high."

Will unplugging the MAP sensor clear P0108?

No. Unplugging it changes what the ECM sees and may set a different code. The fault has to be repaired and the code cleared afterwards.

Can I drive a turbo Encore with P0108?

Short distances, carefully. The ECM may limit power because it cannot trust manifold pressure. Have it checked before long trips.

What's the difference between P0106, P0107 and P0108?

P0106 is performance — the reading is in range but disagrees with GM's model. P0107 is circuit low. P0108 is circuit high. Only P0106 suggests a mechanical problem like a vacuum leak.

Why did the code come back after I replaced the sensor?

Because the fault was almost certainly in the wiring or connector. Test the low reference, 5-volt reference and signal wire back to the ECM.