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Home >> Cadillac >> 2006 >> STS Base, 3.6 7, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - 3.6L - DTC P2178 To U0423 >> DTC P2229 >> Test Description
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Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  This step determines if a condition is present.
  2. 4:  This step is testing the signal circuit. The signal circuit is pulled-up to a voltage, so the DMM should display a voltage within the specified range. If the voltage is high, this indicates the signal circuit is shorted to a voltage. If the voltage is less than the specified range, test the signal circuit for an open.
  3. 6:  This step tests for high resistance in the low reference circuit of the BARO sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM/TCM fuse allows the ECM to power down completely.
DTC P2229

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Control Module Connector End Views  or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
IMPORTANT: If DTC P0118 also sets, refer to DTC P0118 .
  1. Turn ON the ignition, with the engine OFF.
  2. Clear the diagnostic trouble codes (DTCs) with a scan tool.
  3. Start the engine.
  4. Observe the DTC information with a scan tool.
Does the DTC fail this ignition?		 - Go to Step 4  Go to Step 3 
3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 4  Go to Diagnostic Aids
4 
IMPORTANT: The signal circuit of the barometric pressure (BARO) sensor is pulled up to a voltage through a 1 mega-ohm resistor.
  1. Turn OFF the ignition.
  2. Disconnect the BARO sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage between the signal circuit of the BARO sensor and the engine control module (ECM) housing with a DMM.
Is the voltage within the specified range?		 5.2-6.2 V Go to Step 5  Go to Step 7 
5 Measure the voltage between the 5-volt reference circuit of the BARO sensor and the ECM housing with a DMM.
Is the voltage within the specified range?		 4.8-5.2 V Go to Step 6  Go to Step 9 
6 
  1. Turn OFF the ignition.
  2. Remove the ECM/TCM fuse from the underhood electrical center.
    3. NOTE: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.
  3. Measure the resistance between the low reference circuit of the BARO sensor and the ECM housing with a DMM.
Is the resistance less than the specified value?		 5 ohm Go to Step 10  Go to Step 8 
7 Test the signal circuit of the BARO sensor for an open, or for a short to voltage. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 14  Go to Step 11 
8
  1. Disconnect the ECM.
  2. Test the low reference circuit of the BARO sensor for an open, or for a high resistance between the BARO sensor connector and the splice. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 14  Go to Step 11 
9
IMPORTANT: The ECM for this engine is not equipped with 5-volt reference DTCs. The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors.
Test the 5-volt reference circuit of the BARO sensor and all shared 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs .Did you find and correct the condition?		 - Go to Step 14  Go to Step 11 
10 Test for shorted terminals and for poor connections at the BARO sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 14  Go to Step 12 
11 Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 14  Go to Step 13 
12 Replace the BARO sensor. Refer to Barometric Pressure Sensor Replacement .
Did you complete the replacement?		 - Go to Step 14  -
13 Replace the ECM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 14  -
14
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 15 
15 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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