Diagnostics - Vacuum Pump Test

The following items must be performed before performing this diagnostic procedure:

• If the P258A-EVP Relay Control Circuit DTC or a vacuum pressure sensor circuit DTC is present, diagnose those DTCs before continuing.
• Perform the VACUUM SYSTEM LEAK TEST  diagnostic before this diagnostic procedure to determine if the system is leaking, and if so which part of the system is leaking before performing the diagnostics below.

CHECKING THE OPERATION ON THE VACUUM PUMP: This diagnostic is being performed assuming that the VACUUM SYSTEM LEAK TEST was performed and passed both leak checks or that a repair was done and verified fixed. 

1. Pump the brake pedal to lower the vacuum in the brake booster until pedal is hard. Start the engine and verify the Electric Vacuum Pump (EVP) is running. The vacuum pump will be commanded on by the PCM approximately 2 seconds after engine start. If engine vacuum produces enough vacuum in the booster, the pump may not run.  If the EVP is operating, monitor the brake pressure sensor reading while the EVP is running. The pressure should steadily increase until the system reaches the maximum threshold or stabilizes and the EVP turns off. Max threshold should be 65% BARO in park, or 83% BARO while driving at 8 mph or above.
   NOTE:

   If the EVP does not run after engine start, while in park, pump the brake pedal 8-10 times rapidly with the engine running. This will lower the vacuum and activate the vacuum pump. Do not monitor the scan tool at this time.

   1. If the EVP is showing on in the PCM, but can not physically be seen running or the system cannot build vacuum pressure either the electric vacuum pump is failed or there is battery supply or ground circuit issue. Continue to step 2. 
   2. If the EVP does run but cannot increase the vacuum supply either a gross leak is present, the vacuum pressure sensor is faulty, or the vacuum pump is faulty.
      • If the VACUUM SYSTEM LEAK TEST was performed prior to this test and passed, remove the vacuum hose assembly at the brake booster and use a hand vacuum pump to apply vacuum directly to the sensor to verify sensor value changes in the scan tool. If the sensor values do not change while using a hand vacuum pump directly attached to the sensor, replace the vacuum hose assembly with the vacuum pressure sensor. If the system still can not increase vacuum, replace the vacuum pump.
      • If the VACUUM SYSTEM LEAK TEST was not  performed prior to this test, perform that procedure to check for a leak in the system before replacing the electric vacuum pump.
   3. If the EVP runs, increases the vacuum supply into a pass threshold and turns off the system is operating properly.
      • If there was a repair made during the VACUUM SYSTEM LEAK TEST the system is fixed.
      • If the system passed both leak checks in the VACUUM SYSTEM LEAK TEST then the issue is intermittent. Verify a good connection at the EVP, PDC, fuse, EVP relay (if removable) and ground location. If the DTC is still active, the PCM is faulty.
2. Disconnect the EVP harness connector. Load test the battery supply circuit and ground circuit at the EVP harness connector. Connect one lead of the load test tool to the Fused B+ circuit and the other lead of the load test tool to the ground circuit. With the ignition on, the load test bulb should be bright if both circuits are good. To verify that there is no resistance in the circuits being tested, perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the battery terminals if there is no resistance in either circuit. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to STANDARD PROCEDURE .
   1. If the circuits fail the load test, remove the lead connected to the ground circuit and connect it to a good chassis ground. Check the voltage drop across the 3156 bulb of the load test tool again. If the voltage drop is still less than battery voltage, repair the battery supply circuit for an open or high resistance. If the voltage drop is now equal to battery voltage, repair the ground circuit for an open or high resistance.
   2. If the battery supply and ground circuits check good, replace the electric vacuum pump in accordance with the service information.