|Code||Fault Location||Probable Cause|
|P0069|| Manifold absolute pressure (MAP) sensor/barometric pressure (BARO) sensor correlation |
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|MAP sensor, mechanical fault|
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What Does Code P0069 Mean?
The manifold absolute pressure (MAP) sensor is used to measure engine load. The powertrain control module (PCM) sends the MAP sensor a reference voltage and the sensor varies the voltage according to manifold vacuum. The PCM then uses this information to adjust ignition timing and fuel delivery.
An example of a MAP sensor
Vacuum and pressure are inversely proportional (when vacuum goes up, pressure goes down). Because of this, the MAP sensor is able to measure the pressure in the intake manifold to gauge vacuum. Manifold vacuum is a good indicator of engine load. With the engine off, manifold pressure and atmospheric (barometric) pressure are the same. With the engine running, the movement of the pistons and restriction of the throttle plates create vacuum (reduce pressure). When the engine is under heavy load at wide open throttle (WOT), vacuum is nearly zero. At this time, engine pressure and atmospheric pressure are almost the same.
Depending on the elevation, barometric pressure is usually between 28 to 31 inches of mercury (Hg). By comparison, engine vacuum at sea level is between 17-22 in-Hg. This drops approximately 1 in-Hg for every 1000 ft. of elevation. On some vehicles, when the engine is first started, the PCM looks at the MAP sensor to determine barometric pressure. There are other vehicles, however, that use a dedicated BARO sensor. Others still use a combination BMAP sensor.
There are two types of MAP sensors: analog and frequency. The analog type uses a diaphragm and is connected to the intake manifold by a vacuum line. The sensor monitors the movement of the diaphragm and sends a corresponding analog signal back to the PCM. This type of sensor will have three wires: reference, signal and ground. The other type of MAP sensor is the digital, or frequency type, which produces a digital voltage signal instead of an analog signal.
A cut away of an analog MAP sensor
As was mentioned, some vehicles use an independent BARO sensor. These devices are designed to measure only barometric pressure. The BARO sensor is similar to the MAP sensor in design but is more sensitive to changes in atmospheric pressure.
The code P0069 stands for manifold pressure/barometric pressure correlation. The PCM compares BARO sensor and MAP readings at idle. If the difference between the two is greater than specified, the PCM will set a diagnostic trouble code (DTC).
What are the common causes of code P0069 ?
- MAP sensor circuit problem
- BARO sensor circuit problem
- Faulty MAP sensor
- Faulty BARO sensor
- Faulty PCM
What are the symptoms of code P0069 ?
The most common symptom, of course, is an illuminated check engine light. Other symptoms may include surging, rough idle, detonation and loss of power.
How do you troubleshoot code P0069 ?
The following steps will help you diagnose a code P0069:
- Visually inspect the sensors and wiring
The first step is to visually inspect the MAP sensor, its connector and wiring. If the vehicle uses a dedicated BARO sensor you’ll want to inspect that too. Look for corrosion, broken wiring, loose connections, etc. Also check the vacuum line to the sensor for cracks.
- Check MAP sensor operation
Testing the MAP sensor varies depending on which type of sensor you have. This can be determined by measuring the signal voltage; if it never changes from 2.5 volts, the sensor is most likely a frequency type.
- Analog MAP sensor
Analog MAP sensors can be tested with a digital multimeter (DMM) and a handheld vacuum pump. Leave the electrical portion of the MAP sensor connected and disconnect the MAP sensor vacuum hose. Attach the handheld vacuum pump to the MAP sensor nipple.
Next, back probe the MAP sensor signal wire with the red DMM lead and touch the black lead to ground. Pump the vacuum pump while simultaneously watching the DMM. Generally, voltage should decrease as vacuum increases. Consult the manufacturer’s repair information for exact specifications.
Alternately, you can test MAP sensor operation on the vehicle. Back probe the MAP sensor connector with the red meter lead and touch the black meter lead to ground. Turn the ignition key on; the DMM should generally read between 4.6 to 5.0 volts. Next, start the engine and let it idle. The MAP sensors voltage reading should drop to approximately 1 to 2 volts. These readings will vary slightly depending on the altitude. The manufacture’s repair information should be consulted for the exact specifications.
- Digital MAP sensor
Digital MAP sensors can be tested with a digital multimeter (DMM) and a handheld vacuum pump. Leave the electrical portion of the MAP sensor connected and disconnect the MAP sensor vacuum hose. Attach the handheld vacuum pump to the MAP sensor nipple.
Next, back probe the MAP sensor signal wire with the red DMM lead and touch the black lead to ground. Set your meter to the frequency (Hz) setting. Pump the vacuum pump while simultaneously watching the DMM. The frequency should change in regard to the change in vacuum (in most cases Hz will decrease as vacuum increases). Consult the manufacturer’s repair information for exact specifications.
Digital MAP sensor operation is bested with an oscilloscope if one is available. Back probe the MAP sensor connector with the red meter lead and touch the black meter lead to ground. This way the sensors voltage can be read directly. If the sensor is working properly, the voltage signal should change in response to change in manifold vacuum.
Testing digital MAP sensor
- Check the MAP sensor circuit
There should be three wires going to the MAP sensor regardless of whether you’re testing an analog or digital sensor. As was stated earlier, these wires are signal, reference and ground. Start by consulting the wiring diagram for your vehicle to determine which pin on the connector is which. Next, connect the red DMM lead to the battery positive terminal and the black lead to the ground pin. You should see a reading of about 12 volts indicating a good ground. Then, check that the 5-volt reference is getting to the sensor by connecting the red DMM lead to the reference voltage pin and the other to ground. You should see a reading of about 5 volts indicating a good reference voltage. Finally, check that there is continuity to the PCM. You can do this by touching one meter lead to the return signal pin on the sensor connector and the other to signal pin on the PCM. Set your meter to the ohms setting – you should see a value appear on the screen. If instead, your meter read OL, you have an open circuit and will need to trace the factory wiring diagram.
An example of a MAP sensor circuit
- Check the BARO sensor circuit (if equipped)
If the vehicle you’re testing includes a separate BARO sensor, it can be tested in the same fashion as the MAP sensor. Follow the MAP sensor and circuit testing procedures outline above for BARO sensor testing.
If the sensor and circuit test OK, there is only one item left to blame – the PCM. Before you replace the PCM however, it’s a good idea to double check your testing up to this point. PCMs rarely go bad and they are expensive to replace.