OBD-II code P0108 indicates the Manifold Absolute Pressure (MAP) sensor is sending a signal voltage to the powertrain control module (PCM) that is higher than the expected range. The MAP sensor reports engine load by measuring manifold vacuum/pressure, and a persistently high reading points to a sensor, wiring, or circuit problem. The PCM uses this incorrect high-pressure signal to calculate fuel delivery and ignition timing, which can noticeably affect drivability and emissions.
The sensor's internal circuitry can fail or the sensing element can stick, causing it to output an abnormally high voltage. This is the single most common cause of P0108.
If the MAP sensor's ground path is broken, the signal line floats toward the 5-volt reference, producing a sustained high reading. Corroded or loose ground terminals are frequent culprits.
A broken signal wire or one shorted to the 5-volt reference will pull the reported voltage high. Wiring damage from heat, abrasion, or rodent activity is a common source.
Bent pins, pushed-back terminals, moisture intrusion, or corrosion at the MAP sensor harness connector can disrupt the signal and ground paths, leading to an out-of-range high reading.
Less common for a 'high' code, but a blocked reference port in some systems can cause abnormal pressure readings. More typically, vacuum leaks cause low readings rather than high.
Rare. The PCM itself can fail internally, but this should only be considered after sensor and wiring have been thoroughly ruled out. Replacing the computer first is almost always a mistake.
The MAP sensor is the most common cause, so replacement is a reasonable starting point, but the code can also be triggered by wiring, connector, or ground problems. Confirming the fault with a scan tool and a quick voltage check before buying parts avoids unnecessary expense.
Almost never. The PCM is one of the least likely causes of this code, and replacing it without first verifying the sensor, wiring, and grounds is a common and expensive mistake. Shops or sellers recommending a computer replacement without diagnostic evidence should be viewed with skepticism.
A vacuum leak more typically causes the MAP sensor to read lower than expected (less manifold pressure) and is associated with P0107-type behavior. However, in some systems a compromised reference port or related intake issue can contribute to abnormal readings and should be checked.
The vehicle will usually still run, but with reduced fuel economy, rough running, and elevated emissions. Prolonged driving with a rich fuel mixture can contribute to carbon buildup and catalytic converter stress, so the fault should be addressed reasonably soon.