EVR Charging System - Standard Alternator

The generic graphic below shows a single battery system. This graphic is used for the purpose of demonstrating the fundamental operation of the Electronic Voltage Regulation (EVR) system. A dual battery system is wired slightly different but basic charging system control, sense and operation is the same for both.

Courtesy of CHRYSLER GROUP, LLC

EVR DIAGNOSTIC MONITORS:  The following EVR system diagnostics detect failure conditions in different areas of the EVR system:

1. Alternator Field Circuit (P0622):  Detects an open or short condition in the alternator field control (A) circuit. The charging system voltage low or high diagnostics could also detected a failure in this area.
2. Charging System Voltage High (P0563):  Detects that the battery system voltage (B, C, D) is more than 1.0 volt above the target charging voltage for an extended period with the engine running. This diagnostic will give a rapid warning if a hardware failure causes the alternator to be fully fielded or otherwise not controllable by the EVR.
3. Charging System Voltage Low:  Detects that the battery system voltage (B, C, D) is less than the target charging voltage during engine operation. This can be due to a temporary condition that sets a flag but does not set a fault. If the system voltage drops below a calibrated threshold (typically around 9-10 volts) for an extended period, the PCM will set the battery system voltage low fault (P0562)  .
4. Charging System Active (P2503):  Detects that the battery system voltage (B, C, D) is less than the target charging voltage during engine operation due to an open circuit, belt loss or catastrophic alternator failure. Since temporary low voltage can normally exist at idle, the Charging System Active  diagnostic will only run when the engine speed is high enough to assure ample alternator current output to satisfy the electrical loads. If low system voltage is detected the PCM turns off the alternator field for a brief period and watches for system voltage to drop as the alternator output is lost. A failure of the alternator may be detected when the voltage does not drop by a calibrated value. The test requires repeated failures to insure that an erroneous fault is not set.
5. Alternator Sense Line Error (P063A):  Detects that the alternator voltage sense (E) is lower than the system voltage (B, C, D) by a calibrated threshold. This can occur if the alternator voltage sense line has a permanent disconnection due to the break of the wire or an intermittent connection due to corrosion or a loose connection. In this case, the battery system voltage input will be used as control feedback.
6. Alternator Voltage High (P2504):  Detects that the alternator voltage sense (E) is higher than the system voltage (B, C, D) by a calibrated threshold. This can occur due to corrosion or loose connection in the battery system connections.

DIAGNOSING THE COMPLETE CHARGING SYSTEM 

1. Preliminary Checks:
   1. Check the drive belt.
   2. Check the charging system fuse for an open.
   3. Verify there are not any aftermarket accessories that exceed the alternator output.
   4. Verify the battery is not depleted or faulty. A severely depleted can cause charging system issues.
      • Repair any issue found. If the battery is depleted, charge and test the battery with the GR8 Tester before continuing.
      • If the fuse is open, check the positive cables for any damage (rubbed through) or loose connections before replacing the fuse. A loose connection can cause voltage spikes and damage the fuse.
      • If no issues were found, continue to the CHECKING THE STATE OF THE CHARGING SYSTEM section.

CHECKING THE STATE OF THE CHARGING SYSTEM  - Perform the following steps to check the current charging system condition for undercharging, overcharging or functioning normally. In many cases there should be faults associated with the system when there is a failure. This procedure is designed to check the entire system regardless of any DTCs.

1. Turn the engine off. Using the Mopar Scope, connect leads to the following circuits.
   1. Alternator B(+) terminal.
   2. Back probe and connect to the alternator control circuit. Note: The PCM uses a pulse width modulated high side driver for the control. 
   3. Back probe and connect to the alternator sense circuit.
2. With the scan tool also connected, monitor the following data:
   1. Target charging voltage
   2. Voltage sense
   3. Battery voltage
   4. Control duty cycle
3. Start the engine and monitor the scan tool and scope readings. Allow the engine temperature to climb near operating temperature if the vehicle was in a cold environment. The target charging voltage may be low (near battery voltage if there are not significant loads on the system). To raise the target charging voltage and better check the system it may be necessary to turn on some electrical loads such as the headlights and blower motor. Listed below are the expected readings for a normal operating system. They should be very close in value, typically within 0.2v of target charging.
   1. The control duty cycle will typically be between approximately 30% - 40%. If this is being read with a DVOM the average voltage will read between approximately 3.0v-4.0v.
   2. The voltage sense and PCM battery voltage should be within 0.2v of target charging.
   3. The voltage at the alternator B(+) stud will be close the PCM voltage. It may be slightly higher due to the voltage drop through the cables.
   4. The voltage reading at the sense circuit from the alternator should be approximately 3.5v less than the B(+) stud due to the internal resistor inside the alternator. The PCM compensates for this in the scan tool reading.
4. Listed below are the possible results for the state of the charging system:

   1. If the sense voltage and the PCM battery voltage are within 0.2v of target charging and the duty cycle is not at 0% or 100% the system is currently functioning normally.	1. Proceed to the ALTERNATOR FULL FIELD TESTING section below.
   2. If the sense voltage and the PCM battery voltage are less than  the target charging voltage the system is undercharging. In most cases the control duty cycle may be commanded much higher than expected, possibly as high as 100% by the PCM.	2. Proceed to the DIAGNOSING AN UNDERCHARGING CONDITION section below.
   3. If the sense voltage is less than  the target charging voltage, but the PCM battery voltage is within 0.2v of target charging the PCM may be controlling the charging system based on the PCM battery supply voltage due to a fault in the sense circuitry.	3. Proceed to the DIAGNOSING AN OVERCHARGING CONDITION section below and perform the ALTERNATOR SENSE CIRCUIT DIAGNOSTIC.
   4. If the sense voltage and the PCM battery voltage are more than  the target charging voltage the system is overcharging. In the case of an uncontrolled overcharge event the control duty cycle will be commanded to 0% by the PCM.	4. Proceed to the DIAGNOSING AN OVERCHARGING CONDITION section below.

ALTERNATOR FULL FIELD TESTING 

1. Check the alternator full field output. Using the scan tool, run the "Generator Full Field" actuator if available. Actuate the Generator to max percentage. If the actuator is not available, back probe and connect the control circuit to battery positive with a fused jumper while simultaneously measuring voltage at the alternator B(+) terminal. This should full field the alternator. Do not full field the alternator for more than a few seconds at a time. The voltage at the alternator B(+) terminal should increase above 14.0 volts when full fielded if the alternator is functioning properly. The sense voltage and PCM battery voltage on the scan tool should also increase with the alternator output.
   • If the voltage increases as expected, the system and alternator are functioning properly. Check the vehicle for any aftermarket accessories that exceed the alternator output. Verify that the vehicle has the proper rated alternator.
   • Test for an intermittent condition by wiggle testing the wiring and cables to check for a loose connection.

DIAGNOSING AN UNDERCHARGING CONDITION 

1. ALTERNATOR CONTROL CIRCUIT DIAGNOSTIC:  With the engine running check the commanded control duty cycle on the scan tool and at the alternator.
   1. If the duty cycle is 0% at the alternator, verify the duty cycle on the scan tool is not at 0%. the PCM may be commanding this duty cycle due to a fault in the system.
      • If the scan tool is reading 0% the PCM is commanding the duty cycle off. This could be due to another fault in the system. Check the control circuit for a short to ground and the sense circuit for proper operation before condemning the PCM.
      • If the scan tool is showing a commanded duty cycle and there is 0% duty cycle at the alternator, isolate and check the control circuit for an open circuit. If the circuit checks good, the PCM is most likely faulty.
   2. If the duty cycle is above 30% (approximately 3.0v with a DVOM) at the alternator, the PCM is commanding charging. Check the voltage at the B(+) terminal of the alternator to determine if the issue is the alternator or wiring.
      • If the alternator output is within 0.2v of the PCM battery voltage, verify that the alternator case is grounded. If the alternator case ground is good, the alternator is faulty.
      • If the alternator output is above the PCM battery voltage, there is an open between the alternator and the PCM. Check the cables and connections at the alternator and PDC. Check for resistance in the fused B(+) supply circuit to the PCM.
2. ALTERNATOR SENSE CIRCUIT DIAGNOSTIC: 
   1. Compare the voltage on the alternator sense circuit to the voltage on the B(+) terminal. The voltage on the sense circuit should be approximately 3.5 volts less than the B(+) terminal due to the internal resistor in the alternator.
      • If the sense circuit voltage is equal to the B(+) terminal the sense circuit is open, shorted to voltage or the PCM is faulty (not terminating the signal). Unplug the connector and check for voltage on the sense circuit. There should be no voltage present if the circuit is not shorted to voltage. Isolate the circuit and check for an open circuit. If the circuit checks good, the PCM is faulty.
      • If the sense circuit voltage is 0 volts, isolate the circuit and check for a short to ground. If the circuit is not shorted to ground the alternator is faulty.

DIAGNOSING AN OVERCHARGING CONDITION: 

1. Check the commanded control duty cycle on the scan tool.
   1. If the duty cycle is 100%, the PCM is causing the overcharging.
      • The PCM may be compensating for a sense circuit issue instead of using the PCM battery supply as a default. Perform the ALTERNATOR SENSE CIRCUIT DIAGNOSTIC to check the alternator sense circuit in case of a software issue before condemning the PCM.
   2. If the duty cycle is 0% on the scan tool, the system is charging uncontrolled.
      • The duty cycle at the control circuit should be 0%. If there is voltage on the scope pattern, the control circuit is shorted to voltage or the PCM driver is stuck on. Isolate and check the circuit for a short to voltage before condemning a PCM.
      • If there is no voltage on the control circuit at the PCM, the alternator is faulty.