Alternator - smart charge (Ford)

The purpose of this test is to evaluate a Ford-type alternator command signal, feedback signal, and the output current under no load and loaded conditions.

How to perform the test

View connection guidance notes.

  1. Use manufacturer's data to identify the charge circuit functions.
  2. Connect the high amp clamp to PicoScope Channel A select the 200 A scale and zero the clamp.
  3. Connect the clamp around the main positive cable from alternator to battery.
  4. Connect Channel B to the alternator feed-back circuit.
  5. Connect Channel C to the alternator command, signal circuit.
  6. Start the engine and allow it to idle.
  7. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform..
  8. Start the scope to see live data.
  9. With your live waveforms on screen stop the scope.
  10. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.
  11. Repeat the test from step 6 but with as many electrical consumers as possible switched on and engine speed around 2000 to 3000 rpm to increase alternator load.

Example waveform

Engine idle condition

Output signals at high rpm alternator loaded

Waveform notes

These known good waveforms have the following characteristics:

  • At low loads the alternator output current (Channel A) is approximately 14 A. With additional electrical loads, such as those from the heated screen, main beam headlights, and heater blower, the output current increases to 70 A.
  • The alternator feedback signal (Channel B) is a pulse-width-modulated voltage waveform dependent on the alternator current output: with a low load, the waveform is around 0 V for approximately 60% of its cycle duration; at high loads it is around 12 V for approximately 100% of its cycle duration.
  • The alternator command signal from the ECM (Channel C) is a positive-switched pulse-width-modulated voltage waveform. With no load, it remains off, at 0 V. With moderate electrical loads, it is around 13 V for approximately 63% of its cycle duration.

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

The function of a smart alternator is to provide the energy required to power the vehicle’s on-board electrical systems and to replace the charge consumed during cranking and start-up of the engine. This system also balances the needs of the driver, the requirement for maximum torque on hard acceleration or less engine drag during normal operation, for better fuel economy.

The system will also closely manage the battery needs, for example providing the ability to produce a higher charging rate at cold ambient temperatures.

Very nearly all vehicle manufacturers now use smart charging systems but Ford were the first to add the feature to mass market vehicles.

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.


as the ECM is able to better monitor electrical loads and battery temperature, the alternator output can be increased to 18 V in the right conditions. Therefore, it is essential that only silver calcium batteries are used in these systems.

Conventional lead-acid batteries are not suitable.

If the smart alternator controller detects a system fault, the smart charging functionality will be disabled. DTCs set and the engine management and battery warning lights illuminated. Provided the fault is not within the alternator, it will still function conventionally with its output regulated to 14.75 V.


Smart charge systems can be highly intolerant to any alternator that is not manufactured to the original specifications.


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)