Pick-Up Coil


No-Start Diagnosis

A defective pick-up coil may cause a no-start condition or hard starting.

One way to find out if the pick-up coil is defective is to perform a no-start diagnosis of the ignition system. If the pick-up coil is satisfactory, the module may be defective. If the pick-up is defective, replace it.

Resistance Checks

  • The pick-up coil of a magnetic pulse generator or metal detection sensor is also checked for proper resistance using an ohmmeter.
  • Connect the ohmmeter to the pick-up coil terminals to test the pick-up coil for an open or a shorted condition.
  • While the ohmmeter leads are connected, pull on the pick-up leads and watch for a change in the readings. Any change would indicate an intermittent open in the pick-up leads.
  • Most pick-up coils have 150 to 900 ohms resistance, but always refer to the manufacturer's specifications.
  • If the pick-up coil is open, the ohmmeter will display an infinite reading.
  • When the pick-up coil is shorted, the ohmmeter will display a reading lower than specifications.
  • Connect the ohmmeter from one of the pick-up leads to ground to test the pick-up for a short to ground. If there is no short to ground, the ohmmeter will give an infinite reading. Refer to the figure below, which shows that ohmmeter #1 is testing for a short to ground, while ohmmeter #2 is testing the resistance of the pick-up coil.
Ohmmeter-to-pick-up coil test connections. Courtesy of General Motors Corporation - Oldsmobile Division.
  • Another method of measuring the pick-up coil's ac signal is with a voltmeter set on its low voltage scale. the meter registers ac voltage during cranking.
  • Measure this voltage as close to the control module as possible to account for any resistance in the connecting wire from the pick-up coil to the module.
  • If the resistance checks are within specifications, the circuit should be checked with a digital voltmeter.
  • Turn the ignition on and connect the voltmeter across the voltage input wire and ground.
  • Compare the reading to specifications.
  • The voltmeter should also be used to check the resistance across the ground circuit of the distributor.
  • Do this by measuring the voltage drop across the circuit; a drop of more than 0.1 volt is excessive.
  • When the voltmeter is connected between the black/light-blue ground wire and an engine ground, the reading should be less than 0.2 volt.
  • When the voltmeter is connected from the grey/black reference pick-up wire or the tan/yellow sync pick-up wire to an engine ground, the voltmeter should cycle from nearly 0 volt to 5 volts while the engine is cranking.
  • If the pick-up signal is not within specifications, the pick-up is defective.
  • A defective sync pick-up in this distributor should not cause a no-start problem but will affect engine performance.