Alternator - smart charge (Ford)

The purpose of this test is to check a Ford Type smart charging alternator with and without load whilst monitoring ECM control.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use manufacturer data to identify the charge circuit functions.
  2. Connect the high amp current clamp into PicoScope channel A, select the 200 A scale and zero the clamp. Connect the clamp around the main positive cable from alternator to battery.
  3. Connect channel B to the alternator feed-back circuit.
  4. Connect channel C to the alternator command, signal circuit.
  5. Start the engine and allow it to idle.
  6. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  7. Select Go or press the space bar to see live data.
  8. With your live waveforms on screen select Stop or press the space bar to capture the waveforms.
  9. Use the Waveform Buffer and Zoom tools to examine your waveforms.
  10. Repeat the test from stage (5) but with as many electrical consumers as possible switched on and engine rpm around 2000 to 3000. This procedure will place a higher load on the alternator.

Waveform notes

Channel A - alternator current output

It is very important that the clamp is placed on the positive cable from the alternator to the battery. If the clamp is placed on the battery negative, for example, it will show just the balance between the current generated by the alternator and any current consumed by electrical loads. In this case the current reading may not change greatly when additional loads are placed on the system.

In our no-load state the alternator is changing at approximately 14 amps. When we turn on the loads—heated screen, main beam headlights and full speed heater blower—the output current increases to approximately 70 amps.

Channel B - feedback (or monitor) from alternator

This signal is fed back to the engine Electronic Control Module (ECM) and remains a constant square wave or pulse-width-modulated signal. The duty cycle of the signal changes as the output of the alternator increases.

Channel C - load request (or command) signal to alternator

This signal comes from the ECM and changes with load demand. Again it is a square wave or pulse-width-modulated signal. In the no-load example waveform, the signal is idle as the ECM has not detected that any consumer devices are switched on other than the normal engine running. In the full-load example, the signal is active and the alternator's regulator reacts to it by increasing the field current, thus increasing the output current.

The duty cycle on the green trace (alternator feedback) remains virtually unchanged regardless of electrical demand.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Alternator command signal.

Further Guidance

Most manufacturers now employ an electronically controlled alternator system by using the engine's ECM, also referred to as the Powertrain Control Module (PCM), but Ford were one of the first to introduce such a system which they refer to as 'Smart Charging’.

The concept of Smart Charging is actually fairly straightforward. A battery has the capacity to take a slightly higher-voltage charge when cold, so the ECM charges the battery at a slightly higher capacity when cold and balances the charge rate against consumer loads.

The alternator works at maximum capacity only when absolutely necessary and the battery is kept in a constant and healthy state of charge. Battery temperature is estimated from the intake air temperature sensor, which is a good indication of the temperature under the hood.

Battery type warning: Ford specify a silver calcium battery for use with this system. A conventional lead-acid battery is not suitable.


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • 200 A / 2000 A (high amps) DC current clamp


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Alternator - smart charge (Ford)