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Home >> Chevrolet >> 2004 >> Optra Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - 1.8L (L79) - DTC P0301 To DTC P1114 >> DTC P0502 >> Test Description
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Test Description

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

  1. 2:  The permanent magnet generator only produces a signal if the drive wheels are turning greater than 8 km/h (5 mph). This step determines if DTC P0502 is the result of a hard failure or an intermittent condition.
Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics (European Emissions)  or  Engine Controls Schematics (Non European Emissions) 
Connector End View Reference:  Engine Controls 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 
  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTCs with a scan tool.
    3. NOTE: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.
  3. Raise and support the drive wheels.
  4. Start and idle the engine.
  5. Engage the transmission into 2nd gear.
  6. Observe the Vehicle Speed Sensor parameter with a scan tool.
Is the vehicle speed more than the specified value?		 0 km/h (0 mph) Go to Step 3  Go to Step 4 
3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. 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
  1. Turn OFF the ignition.
  2. Disconnect the vehicle speed sensor (VSS) connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage at the signal circuit of the VSS with a DMM.
Is the voltage within the specified range?		 9-11 V Go to Step 5  Go to Step 7 
5 Measure the voltage at the ignition 1 voltage circuit of the VSS with a DMM.
Is the voltage within the specified range?		 11-14 V Go to Step 6  Go to Step 11 
6 Measure the resistance between the ground circuit of the VSS and battery ground with a DMM.
Is the resistance less than the specified value?		 5 Ω Go to Step 8  Go to Step 12 
7 Test the VSS signal circuit for the following conditions:
  • An open
  • A short to ground
  • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 10 
8
  1. Remove the VSS.
  2. Inspect the VSS and the transmission for the following conditions:
    • Incorrect VSS
    • VSS damage
    • Excessive VSS to speed sensor rotor gap
    • Incorrect VSS rotor alignment
    • VSS rotor damage
  3. Repair any of the above conditions, as necessary.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 9 
9 Test for shorted terminals and poor connections at the VSS. 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 15  Go to Step 13 
10 Test for shorted terminals and poor connections at the engine control module (ECM). 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 15  Go to Step 14 
11 Repair the ignition 1 voltage circuit between the VSS connector and the fuse for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 15  -
12 Repair the VSS ground circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 15  -
13 Replace the VSS.
Did you complete the replacement?		 - Go to Step 15  -
14 Replace the ECM. Refer to Engine Control Module Replacement .
Did you complete the replacement?		 - Go to Step 15  -
15
  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 16 
16 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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