How to Troubleshoot a P0105

You can trace the cause of a P0105 in your car using a few tools at home.

The MAP (manifold absolute pressure) sensor monitors pressure inside the intake manifold. Your vehicle's computer stays in constant communication with the MAP to adjust fuel, spark timing and perform other operations. Whenever the MAP signals or circuit deviate from other sensors' signals it works in unison with, your computer stores a P0105 trouble code, indicating a MAP problem. Troubleshoot the P0105 code and find the cause by checking some possible involved components, including your MAP sensor.

Things You'll Need

• 2 feet rubber hose
• Digital multimeter
• Hand vacuum pump
• Vehicle service manual

Instructions

1. Locate the MAP and TPS sensors in your vehicle. The MAP sensor connects to the intake manifold on top of your engine with a vacuum hose. It is a small, black square box with an electrical connector on it. The TPS sensor is attached to one side of the throttle body on the intake manifold, and is a square box with an electrical connector.

2. Check the vacuum hoses on your engine, including the MAP vacuum hose, for cracks, damage, loose connections or obstruction. A vacuum leak can cause the MAP sensor to read manifold pressure that does not correspond to the engine load indicated by the TPS. Replace any damaged or blocked vacuum hoses.

3. 

   Use a small piece of rubber hose to locate vacuum leaks in your engine.

   Start the engine and listen for a hissing sound indicating a vacuum leak. Using a rubber hose of about two feet in length, place one end of the hose against your ear and move the other end around the engine to locate a possible leak. A vacuum leak caused by a damaged cylinder head or throttle body gasket may cause the MAP to conflict with the TPS or other sensor's signal as well. Turn off the engine.

4. Check the electrical connections and wiring on the MAP and TPS sensors. A loose, bad connection or damaged wiring will make these sensors inoperable.

5. 

   Use a digital multimeter to check the MAP and TPS electrical wires and voltages.

   Check the wiring on the MAP and TPS sensors for open circuits or shorts using a digital multimeter, following the troubleshooting procedures in your vehicle service manual.

6. Unplug the electrical connector from the MAP sensor. Connect the black lead of a digital voltmeter to the ground pin on the MAP sensor and the red lead of the meter to the signal pin on the sensor. Use your vehicle service manual to locate these pins on your sensor. Set your digital meter to 20 volts on the DCV (direct current voltage) scale.

7. Disconnect the vacuum hose from the MAP sensor and connect a hand vacuum pump to its vacuum port.

8. Turn on your digital meter and read the meter's display. It should be about 4.6 to 4.8 volts. Apply five inches Hg vacuum pressure to the sensor using the hand vacuum pump. This time, your meter should register about 3.75 volts. Apply 20 inches Hg vacuum pressure to the sensor using the hand vacuum pump. This time, your meter should register about 1.0 volts. If you see different voltage readings from the ones indicated here, replace the MAP sensor.

9. Troubleshoot your TPS sensor as indicated in your vehicle service manual using your digital meter. If your TPS is working properly, there might be a problem with your ECM (electronic control module) which is the vehicle computer. Take your vehicle to an auto repair shop, if necessary.

Tips & Warnings

• The vehicle service manual for your specific make and model will help you locate and identify most components and their electrical circuits in your car. It even helps you troubleshoot and test most sensors and wiring circuits for trouble as well.

References

• "The Haynes Emissions Control Manual"; Mike Stubblefield and John H. Haynes; 2001
• "Modern Automotive Technology"; James E. Duffy; 2003