P0108 means the signal from the manifold absolute pressure (MAP) sensor has gone above the highest voltage the engine computer accepts as possible. It is a circuit code. It does not say the engine has too little vacuum. It says the reading has left the range a working sensor can produce, and that points to the sensor, its wiring or its software rather than to the engine. This article explains what sets P0108, the six real causes in order of likelihood, and how a couple of simple meter checks tell you which one you have before you buy a sensor.
Start with the table, then read the triage note under it.
| Cause | Telltale Sign | Typical Cost |
|---|---|---|
| Engine software needing an update | A service bulletin covers your engine for P0108 | $0 to $200 |
| Failed MAP sensor | Reading stays high with the wiring proven good; a bulletin may cover your sensor | $60 to $300 installed |
| Open sensor ground (low reference) circuit | Signal reads near the full 5-volt reference at all times | $50 to $300 |
| Signal wire shorted to a voltage source | Reading stays high even with the sensor unplugged | $100 to $300 |
| Corroded or water-damaged connector | Code comes and goes with weather, washing or engine movement | $0 to $150 |
| Wrong replacement sensor, or a PCM fault | Code started after a sensor was replaced, or everything else tests good | $60 to $1,000 |
Have it checked soon, and avoid heavy loads or towing, if the engine is running badly, smoking black or has gone into reduced power. On many engines the MAP reading helps set fuelling and ignition timing, and an engine that believes it is under heavy load may run rich. Most engines substitute a default value once P0108 sets, so many drive reasonably well. If yours does, it is safe to drive while you arrange the diagnosis.
What P0108 Actually Means
The MAP sensor measures the absolute pressure inside the intake manifold. The engine computer supplies it with a 5-volt reference and a ground, and the sensor returns a signal voltage that rises as manifold pressure rises. At a warm idle, a healthy non-turbo engine has strong manifold vacuum, so the pressure and the signal voltage are low. At wide-open throttle, or with the engine off, manifold pressure is close to the outside air pressure and the voltage is high. On turbocharged engines it climbs further still under boost, which is why those engines use sensors with a wider range.
The computer uses that signal to calculate engine load. On some engines it drives fuelling directly, and on engines with a mass airflow sensor it acts as a cross-check. So the computer watches the signal for plausibility. P0108, “Manifold Absolute Pressure Sensor Circuit High”, sets when the signal voltage stays above a calibrated upper limit, close to the full reference voltage, for longer than a set time. P0107 is the same fault in the low direction.
Why P0108 Is Not the Same as P0106
This is the distinction that saves money. A MAP sensor can only produce voltages within the range of pressures it is built to measure. A mechanical problem, such as a split vacuum hose to a remote-mounted sensor, a large vacuum leak or low vacuum from a timing or valve problem, changes the pressure the sensor sees. But the sensor still reports that pressure within its normal range. Those faults usually show up as P0106, the MAP range/performance code, where the reading is possible but does not make sense for the conditions.
P0108 means the voltage has gone past anything a working sensor would report. That is the signature of an electrical fault: a lost ground, a signal wire touching a voltage source, a sensor that has failed internally, or software misjudging the reading. So the first tools for P0108 are a multimeter and a check for bulletins, not a smoke machine or a vacuum gauge. The site’s guide to vacuum leak symptoms and how to find one is the better starting point if you have P0106 instead.
Symptoms You May Notice Alongside the Code
It depends on how much your engine relies on the MAP signal. Many engines show only the check engine light once they switch to a default value. Others run rich, idle roughly, hesitate or lose power, and some trigger other warnings as systems that use engine load data shut themselves down. Ford’s service bulletin 19-2183 for 2018 to 2019 Explorer, Flex, Taurus and MKT models with the 3.5L EcoBoost lists the check engine light, the powertrain malfunction (wrench) lamp, a “Service AdvanceTrac” message, a “Hill Start Assist Not Available” message and a lack of power alongside P0107, P0108 or P0109.
1. Engine Software Needing an Update
Check this first because it can be free and needs no parts. Chrysler’s service bulletin 18-028-12 covers P0108 on 2012 Dodge Durango and Jeep Grand Cherokee models with the 3.6L engine, and states that “updating the software will correct the condition.” Volkswagen issued bulletin 2030688 for the 2012 Routan with the same 3.6L engine built before June 25, 2012, with the same PCM software update as the fix. A dealer can check your VIN for open bulletins in a few minutes.
2. Failed MAP Sensor
The sensor itself can fail internally and drive its output high. The Ford bulletin above attributes the codes to “a faulty manifold absolute pressure and temperature (MAPT) sensor” and replaces it. GM’s preliminary information PIP5787A covers 2021 Escalade, Silverado, Sierra, Tahoe, Suburban, Yukon, Express and Savana models built between January 1 and February 15, 2021 that set P00C7 with P0106 and P0108. It names “a faulty Manifold Absolute Pressure (MAP) sensor” as the cause.
Before buying one, prove it with the checks in the diagnostic section below. A sensor replaced on suspicion while the real fault is a broken ground will set the same code within minutes.
3. Open Sensor Ground (Low Reference) Circuit
This is the classic wiring cause. The sensor needs a good ground to pull its signal down. If that ground, often called the low reference circuit, breaks or corrodes, the signal floats up toward the 5-volt reference and reads as maximum pressure all the time. With the key on and the engine off, back-probing the connector shows it quickly. The ground terminal should read within a few tenths of a volt of battery negative. A reading well above that, or an open circuit on a resistance check back to the computer, is the fault.
4. Signal Wire Shorted to a Voltage Source
If the signal wire chafes against the 5-volt reference wire or another powered circuit, the computer sees that voltage on its input no matter what the sensor is doing. The giveaway is that the reading stays high even with the sensor unplugged. Most engine computers pull an unplugged MAP signal low, so an open signal normally sets P0107, not P0108. Look for damage where the harness passes brackets, the valve cover or hot parts, and anywhere the engine has recently been worked on.
5. Corroded or Water-Damaged Connector
The MAP sensor usually sits on top of the intake manifold, where it is exposed to engine heat, washing and any water running off the cowl. Corroded terminals, a cracked connector body or a terminal that has backed out of its housing can break the ground or bridge two terminals, and either can set P0108. An intermittent code that appears after rain, a car wash or engine cleaning points here. Unplug it, inspect both halves, and check that each terminal grips firmly.
6. Wrong Replacement Sensor, or a PCM Fault
MAP sensors look alike across models but are built for different pressure ranges. A turbocharged engine needs a sensor that can read well above atmospheric pressure. A sensor designed for a non-turbo engine will reach the top of its output as soon as boost builds, which the computer can read as circuit high. If P0108 started after a sensor was replaced, confirm the part number matches the original.
The engine computer itself is the least likely cause. Diagnose it only after the sensor, the reference voltage, the ground and the signal wire all test good. Check for software updates before replacing it.
Diagnosing P0108 in the Right Order
- Record all codes and the freeze frame. A reference-voltage code, or codes for other sensors that share the same 5-volt supply, changes the diagnosis.
- Check for service bulletins and software updates by VIN.
- Compare MAP with barometric pressure, key on, engine off. With the engine stopped, manifold pressure equals outside air pressure, so the MAP reading should match the barometric reading on a scan tool, or local air pressure. A reading far above that, or pinned at its maximum, confirms the fault is present now.
- Unplug the sensor and watch the reading. If it drops to its minimum, the wiring and computer are probably fine and the sensor, or its ground, is pulling the signal high. If it stays high, look for a short on the signal wire.
- Back-probe the connector. Check for about 5 volts on the reference terminal and a good ground on the low reference terminal, both with the key on.
- Inspect the connector and harness for corrosion, water and chafing.
- Only then replace the sensor, with the correct part number for your engine.
Repair Cost
Typical costs, labelled as typical because sensor prices and access differ between engines:
- PCM software update: often free under a bulletin or the emissions warranty, otherwise up to about $200.
- MAP sensor replacement: roughly $60 to $300 installed. On most engines it is a short job on top of the intake manifold, and combined pressure-and-temperature sensors cost a little more.
- Connector cleaning or repair: free to about $150.
- Wiring repair: roughly $100 to $300, depending on where the fault is.
- Engine computer replacement: rarely needed; roughly $500 to $1,000 including programming.
Can You Keep Driving With a P0108 Code?
Often yes, carefully. Once P0108 sets, most engine computers stop trusting the MAP reading and switch to a default value or to other sensors, so the engine may run nearly normally. How well depends on how much your engine relies on the MAP sensor. On engines that calculate fuelling from it, drivability can suffer noticeably. Where a turbocharged engine uses it for boost control, power may be limited.
Do not ignore it for long. A rich-running engine wastes fuel, fouls spark plugs and can overheat the catalytic converter, and the lit check engine light hides any new fault. Avoid towing or heavy loads until it is fixed, and stop if the check engine light starts flashing.
Related Codes
- P0105: MAP sensor circuit malfunction, a general circuit fault.
- P0106: MAP sensor range/performance. The reading is possible but does not match conditions, which is where vacuum leaks and hose faults usually show up. See the P0106 guide.
- P0107: MAP sensor circuit low, the opposite direction to P0108. It is usually an open signal wire or a short to ground.
- P0109: MAP sensor circuit intermittent. It often has the same connector causes as P0108.
- P0102 and P0103: mass airflow sensor circuit low and high. These are the MAF equivalent on engines that use both sensors. See the P0102 guide and the P0101 guide for the MAF range/performance code.
- P0113: intake air temperature sensor circuit high. It follows the same electrical logic as P0108, where a high input often means an open circuit. See the P0113 guide. On engines with a combined MAP and temperature sensor, the two codes can come from the same part.
Frequently Asked Questions
What does the P0108 code mean?
P0108 means the MAP sensor signal is higher than the engine computer accepts as possible. It is an electrical code, usually caused by a failed sensor, an open ground, a shorted signal wire, a corroded connector or software, not by a vacuum leak.
Can a vacuum leak cause P0108?
Rarely. A vacuum leak or disconnected hose changes the pressure the sensor sees, but it still reports it within its normal range. That usually sets P0106. P0108 points at the sensor, its wiring or its software.
Is it safe to drive with a P0108 code?
Often, for a short time. Most engines switch to a default value and run reasonably well. Avoid towing and heavy loads, and have it checked promptly if the engine runs rough, smokes black, loses power or the check engine light flashes.
Should I just replace the MAP sensor?
Not before a quick test. With the key on and engine off, the MAP reading should match barometric pressure. Unplug the sensor: if the reading drops, the sensor or its ground is at fault. If it stays high, the signal wire is shorted, and a new sensor will not help.
What is the difference between P0107 and P0108?
Both are MAP sensor circuit faults. P0107 means the signal is too low, usually an open signal wire or a short to ground. P0108 means it is too high, usually a failed sensor, an open sensor ground or a signal wire shorted to voltage.
How much does it cost to fix P0108?
From nothing for a software update or a cleaned connector, to about $60 to $300 for a MAP sensor installed, and $100 to $300 for wiring repairs. Engine computer replacement is rarely needed.
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