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High MAP voltage tricks the ECM into thinking vacuum is very low. The ECM may respond by adding too much fuel, causing a rich condition. Watch for black smoke, poor MPG, and fouled plugs along with this code. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0108 MAP sensor high voltage (short or failed sensor)
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0108 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
45%
#1 - Most Likely
Short to Voltage in Signal Wire
The MAP sensor signal wire has shorted to a 12V source, sending near-battery voltage to the PCM. The PCM interprets this as extremely low manifold vacuum (high load). Inspect the harness for areas where the wire could contact a positive circuit.
🔩 Part
$5–$30
👨🔧 Labor
$50–$150
⚡ DIY Difficulty
Medium
35%
#2 - Check First
Failed MAP Sensor Reading High
The sensor element has failed and is stuck outputting a high voltage regardless of actual manifold pressure. Most common after oil or moisture contamination of the sensor body.
🔩 Part
$30–$100
👨🔧 Labor
$30–$80
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Plugged Vacuum Port (No Vacuum to Sensor)
With no vacuum reaching the sensor, it sees atmospheric pressure at all times, resulting in a constant high-output signal. Disconnect the vacuum line and blow it out.
🔩 Part
$0
👨🔧 Labor
$20–$40
⚡ DIY Difficulty
Easy
8%
#4 -
Faulty PCM MAP Input Circuit
Rarely, the PCM input circuit itself is damaged and reads high even with a good sensor. Confirm by testing a substitute sensor and checking signal voltage at the PCM connector directly.
🔩 Part
$300–$800
👨🔧 Labor
$100–$200
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Check Signal Wire for Short to Power - With the sensor unplugged, use a multimeter to check for voltage on the signal terminal in the connector harness side. Any voltage present indicates a short in the wiring.
- Measure MAP Sensor Output - Reconnect sensor and backprobe the signal wire at idle. Should read 1–1.5V. Above 4V at idle with no large vacuum leaks indicates sensor failure.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need