In this tutorial I'll explain what a P0108: MAP Sensor Circuit High Voltage trouble code means. I'll also talk about some of the tests you can perform to find its cause and solution.
Contents of this tutorial:
You can find this tutorial in Spanish here: Código P0108 ¿Qué Significa? (1996-1999 3.8L V6 Buick, Chevrolet, Pontiac, Olds) (at: autotecnico-online.com).
APPLIES TO: This tutorial, on the P0108 OBD II trouble code, applies to the following vehicles:
- 3.8L Buick LeSabre: 1996, 1997, 1998, 1999.
- 3.8L Buick Park Avenue: 1996, 1997, 1998, 1999.
- 3.8L Buick Regal: 1996, 1997, 1998, 1999.
- 3.8L Buick Riviera: 1996, 1997, 1998, 1999.
- 3.8L Chevrolet Lumina: 1998, 1999.
- 3.8L Chevrolet Monte Carlo: 1998, 1999.
- 3.8L Oldsmobile 88 (Eighty-Eight): 1996, 1997, 1998, 1999
- 3.8L Oldsmobile 98 (Ninety-Eight): 1996
- 3.8L Oldsmobile Intrigue: 1998, 1999
- 3.8L Oldsmobile LSS: 1996, 1997, 1998, 1999
- 3.8L Oldsmobile Regency: 1997, 1998
- 3.8L Pontiac Bonneville: 1996, 1997, 1998, 1999
- 3.8L Pontiac Grand Prix: 1997, 1998, 1999
What Does Trouble Code P0108 Mean?
A P0108: MAP Sensor Circuit High Voltage sets when the following conditions are met:
- No throttle position sensor (TPS) codes are present.
- Engine speed less than 900 RPM (engine at idle) and engine has been running between 0.5 to 2 seconds.
- The MAP sensor's signal voltage is stuck at a value greater than 4.2 Volts while the engine is running.
To better understand why this is a problem, take a look at the section: What Does The MAP Sensor Do?
Common Symptoms Of A P0108 Trouble Code
The manifold absolute pressure (MAP) sensor is tasked with measuring the vacuum pressure in the intake manifold.
This vacuum pressure measurement is then used by the fuel injection computer to calculate engine load.
Since it's an important component of the engine management system, when it fails, engine performance will suffer. You'll see one or more of the following symptoms:
- Check engine light illuminated.
- Rough or low idle.
- Very high idle.
- Engine may start and stall.
- Little to no acceleration.
- Black smoke comes out of the tailpipe when the engine is running.
What Does The MAP Sensor Do?
The MAP sensor's job is to inform the fuel injection computer the intake manifold's vacuum pressure when the engine is running.
When the engine is idling and the throttle plate is closed, intake manifold pressure is high.
This high intake manifold pressure will cause the MAP sensor to produce a low voltage signal (usually around 2 Volts DC).
As you step on the accelerator pedal, the throttle plate opens and the engine accelerates. This causes a decrease in intake manifold vacuum pressure.
This low intake manifold pressure will cause the MAP sensor to produce a high voltage signal. At wide open throttle (like when you trying to run that red light), the MAP sensor produces a voltage around 4 Volts DC.
As long as the fuel injection computer sees the MAP sensor voltage signal decreasing/increasing, as you step on or off the accelerator pedal, it knows that the MAP sensor is functioning correctly.
What Causes A P0108 Trouble Code?
The most common cause of a P0108 trouble code is generally a bad MAP sensor.
Other things that can cause a P0108 trouble code are:
- The MAP sensor signal wire has a short-circuit to voltage problem.
- A bad MAP sensor connector causing an intermittent false connection.
- The MAP sensor's vacuum inlet is plugged.
- The MAP sensor's Ground wire has an open-circuit problem between the MAP sensor connector and the PCM connector.
- Bad fuel injection computer (although very rare).
- Major vacuum leak.
How To Diagnose And Repair A P0108 Trouble Code
Troubleshooting and resolving a P0108 involves testing the MAP sensor.
The test involves confirming that the MAP sensor is stuck at a voltage greater thatn 4.2 Volts as you apply/release vacuum to the sensor.
Then making sure that the MAP sensor is getting 5 Volts and Ground from the fuel injection computer.
You can conclude that the MAP sensor is bad, and needs to be replaced, if your test results confirm:
- That the MAP sensor signal voltage DOES NOT decrease/increase as you apply/release vacuum to the sensor.
- That the MAP sensor is getting 5 Volts.
- That the MAP sensor is getting Ground.
Testing the MAP sensor can be done with a simple multimeter (no scan tool required). You can find the test here: How To Test The MAP Sensor (1995-1999 3.8L V6 Buick, Chevrolet, Pontiac, Olds).
Where To Buy The MAP Sensor And Save
There are a lot of knock-off parts that you can buy on the cheap, but that'll only last a few weeks. The following links will help you comparison shop for original equipment (OE) MAP sensor:
More 3.8L V6 GM Tutorials
You can find a complete list of 3.8L GM V6 tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The MAF Sensor (GM 3.8L V6 1996-2005).
- How To Test A Does Not Crank Condition -Case Study (GM 3.8L).
- GM 3.8L Ignition Control Module And Crank (3X, 18X) Sensor Test.
- How To Test The Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L).
If this info really saved the day, buy me a beer!