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Home >> Buick >> 2004 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls 3.1L (Troubleshooting & Diagnosis) >> Engine Controls >> Manifold Absolute Pressure (MAP) Sensor Diagnosis >> Test Description

Test Description

The number below refers to the step number on the diagnostic table.

  1. 4:  This step tests the MAP sensor's ability to correctly indicate BARO.
  1. 12:  The measurement noted in this step will be used in subsequent steps if the measurement does not exceed the specified value.
  1. 15:  This step calculates the resistance in the 5-volt reference circuit.
  1. 16:  This step calculates the resistance in the low reference circuit.
Manifold Absolute Pressure (MAP) Sensor Diagnosis

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Controls Connector End Views  or  Powertrain Control Module (PCM) Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Inspect for the following conditions:
  • Disconnected, damaged, or incorrectly routed vacuum hoses
  • Manifold absolute pressure (MAP) sensor disconnected from the vacuum source
  • Restrictions in the MAP sensor vacuum source
  • Intake manifold vacuum leaks

Did you find and correct the condition?		 - Go to Step 28  Go to Step 3 
3
IMPORTANT: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable.
Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool?		 - Go to Step 4  Go to Step 5 
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool.
  3. Observe the MAP sensor pressure in the known good vehicle with a scan tool.
  4. Compare the values.
Is the difference between the values less than the specified value?		 3 kPa Go to Step 6  Go to Step 10 
5
IMPORTANT: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool. Refer to Altitude vs Barometric Pressure .
  3. The MAP sensor pressure should be within the range specified for your altitude.
Does the MAP sensor indicate the correct barometric pressure?		 - Go to Step 6  Go to Step 10 
6
  1. Observe the MAP sensor pressure with a scan tool.
  2. Start the engine.
Does the MAP sensor pressure change?		 - Go to Step 7  Go to Step 10 
7
  1. Turn OFF the ignition.
  2. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness.
  3. Connect a J 23738-A  Mityvac to the MAP sensor.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the MAP sensor pressure with the scan tool.
  6. Apply vacuum to the MAP sensor with the J 23738-A  in 1 in Hg increments until 15 in Hg is reached. Each 1 in Hg should decrease MAP sensor pressure by 3-4 kPa.
Is the decrease in MAP sensor pressure consistent?		 - Go to Step 8  Go to Step 10 
8 Apply vacuum with the J 23738-A  until 20 in Hg is reached.
Is the MAP sensor pressure less than the specified value?		 34 kPa Go to Step 9  Go to Step 10 
9 Disconnect the J 23738-A  from the MAP sensor.
Does the MAP sensor pressure return to the value observed in step 4 or 5?		 - System OK Go to Step 26 
10 Test for an intermittent and for a poor connection at the MAP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 11 
11
  1. Disconnect the MAP sensor electrical connector.
  2. Observe the MAP sensor parameter with the scan tool.
Is the voltage less than the specified value?		 0.1 V Go to Step 12  Go to Step 18 
12  Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Note the measurement as "Supply voltage".
Is the voltage more than the specified value?		 5.2 V Go to Step 19  Go to Step 13 
13 Is the voltage more than the specified value? 4.8 V Go to Step 14  Go to Step 20 
14
  1. Disconnect the harness connector from the engine coolant temperature (ECT) sensor.
  2. Connect a test lamp and a DMM in series between the 5-volt reference circuit and the low reference circuit of the MAP sensor, at the harness connector.
  3. Measure the amperage, with the DMM. Note the measurement as "Amperage".
Is the amperage equal to the specified value?		 0 mA Go to Step 23  Go to Step 15 
15 
  1. Remove the DMM from the circuit.
  2. Connect the test lamp between the 5-volt reference circuit and the low reference circuit of the MAP sensor, at the harness connector.
  3. Measure the voltage from the 5-volt reference circuit at the test lamp to a good ground, with the DMM. Note the measurement as "Load voltage drop".
    4. IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units. For example, volts/amps or millivolts/milliamps.
  4. Subtract the "Load voltage drop" from the "Supply voltage". Note the result as "Supply voltage drop".
  5. Divide the "Supply voltage drop" by the "Amperage".
Is the result more than the specified value?		 5 Ω Go to Step 21  Go to Step 16 
16 
  1. Measure the voltage from the low reference circuit of the MAP sensor at the test lamp to a good ground, with the DMM. Note the result as "Low reference voltage drop".
    2. IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units. For example, volts/amps or millivolts/milliamps.
  2. Divide the "Low reference voltage drop" by the "Amperage".
Is the result more than the specified value?		 5 Ω Go to Step 24  Go to Step 17 
17
  1. Remove the test lamp.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the MAP sensor, at the harness connector.
  3. Observe the MAP sensor parameter with the scan tool.
Is the voltage more than the specified value?		 4.9 V Go to Step 26  Go to Step 22 
18 Test the MAP sensor signal circuit between the powertrain control module (PCM) and the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
19 Test the 5-volt reference circuit between the PCM and the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
20 Test the 5-volt reference circuit between the PCM and the MAP sensor for an open or for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
21 Test the 5-volt reference circuit between the PCM and the MAP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
22 Test the MAP sensor signal circuit between the PCM and the MAP sensor for an open or for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
23 Test the low reference circuit between the PCM and the MAP sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
24 Test the low reference circuit between the PCM and the MAP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
25 Test for shorted terminals and for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 27 
26 Replace the MAP sensor. Refer to Manifold Absolute Pressure (MAP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 28  -
27 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Did you complete the replacement?		 - Go to Step 28  -
28
  1. Reassemble the vehicle as necessary.
  2. Clear the DTCs with the scan tool.
  3. Start the engine.
  4. Operate the system in order to verify the repair.
Did you correct the condition?		 - Go to Step 29  Go to Step 2 
29 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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