LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Jaguar >> 2002 >> XJR Base >> Repair and Diagnosis >> Electrical >> Charging Systems >> Generators & Regulators >> On-Vehicle Testing >> Generator Output Test
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Generator Output Test

NOTE: If the cooling fans operate during generator test, the large current demand will overload generator and cause engine to stall. If battery charge is low the voltage will momentarily increase when the battery is disconnected. The maximum that the voltage can increase to is 25 volts for a maximum of 200 mS.
NOTE: If a known good battery is used for generator testing, voltage measured between terminals must be approximately 12.8 volts. Battery cannot have been on a charger within 12 hours of testing.
    NOTE: If generator is inoperative, engine will stall when negative battery cable is disconnected.
  1. Remove battery cover. Ensure all electrical loads are off and that engine is cool. Start engine and allow to idle. With the engine running, disconnect negative battery cable at the battery. Measure voltage between negative battery cable and battery positive terminal. See Fig 1 . Generator output voltage should be 13-15 volts. This indicates system voltage with the battery out of the circuit. When voltage has been measured, shut engine off. Go to next step.
  2. Connect the negative battery cable to the battery. Repeat test in step 1)  using frame connection point for negative battery cable. See Fig 2 . Generator output voltage should be 13-15 volts. When voltage has been measured, shut engine off. The should be hardly a detectable difference in generator output voltage compared to reading taken in previous step. If there is a detectable difference in voltage, clean cable connections or replace cable. If voltage is not within specification, go to next step.
  3. Check that all terminals are clean and tight. See Fig 3 . If the IG terminal connection on the 3-pin connector is faulty, the generator will never function correctly. Disconnect the 3-pin connector at the rear of the generator. With the engine off, ignition on, use a DVOM to check for battery voltage between the center pin on the 3-pin plug connector and a good vehicle ground. See Fig 4 . If battery voltage is not present, check continuity between generator 3-pin connector center terminal and fuse No. 5 (10 amp). See WIRING DIAGRAMS  . Repair as necessary. If battery voltage is present, switch off the ignition, reconnect the 3-pin connector. Go to next step.
  4. Ensure all electrical loads are off and that engine is cool. Start engine and allow to idle. With the engine running, disconnect negative battery cable at the battery. Measure voltage between negative battery cable and battery positive terminal. See Fig 1 . Generator output voltage should be 13-15 volts. If voltage is still out of specification, replace generator. See GENERATOR  under REMOVAL & INSTALLATION.
Fig 1: Identifying System Voltage Test Points (Battery Negative Cable At Battery)
G00311054Courtesy of JAGUAR CARS, INC.
Fig 2: Identifying System Voltage Test Points (Battery Negative Cable At Frame)
G00311055Courtesy of JAGUAR CARS, INC.
Fig 3: Identifying Generator Electrical Connections
G00311056Courtesy of JAGUAR CARS, INC.
Fig 4: Identifying Generator 3-Pin Connector Terminals
G00311057Courtesy of JAGUAR CARS, INC.
scientia non olet · About LEMON Manuals