LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> BMW >> 1987 >> 635CSi Standard >> Repair and Diagnosis >> Engine Performance >> System >> MOTRONIC CEC System >> Testing >> Test 7: Idle Control Unit
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test 7: Idle Control Unit

  1. Check power supply to Idle Control Unit (ICU). Pull connector plug off of ICU and connect volt/ohmmeter between terminal No. 2 of plug and ground. Start engine. Voltmeter should read battery voltage. If not, repair circuit.
  2. If voltage is correct, check ground connection of ICU. Connect volt/ohmmeter between terminal No. 4 of plug and ground. Ohmmeter should read infinity. If not, trace circuit and repair wiring.
  3. If resistance is correct, check speed signal to ICU at terminal No. 3 of ICU plug using BMW Test Meter (22 13 100 ). If signal is not correct, trace circuit and repair wiring.
  4. If signal is correct, check for ground at terminal No. 6 of ICU. Connect volt/ohmmeter between terminal No. 6 of ICU plug and ground. With coolant temperature below 106°F (41°C), resistance should be zero. With coolant temperature above 117°F (47°C), resistance should be infinite. If values are incorrect, check coolant temperature switch. See TEST 11  . If switch is good, trace idle control unit circuit and repair wiring. If resistance values are correct, go to next step.
  5. On vehicles equipped with automatic transmission, check for battery voltage at terminal No. 7 of plug with ignition on and transmission shift lever in "N" position. If no voltage is present, trace circuit and repair wiring. If voltage is present at terminal No. 7, check for battery voltage at terminal No. 8 with shift lever in "P" position. If no voltage is present, trace circuit and repair wiring. If reading is correct, go to next step.
  6. On vehicles with air conditioning, check for battery voltage at terminal No. 9 of A/C plug with air conditioner on. Trace circuit and repair wiring if voltage is incorrect. If reading is correct, go to next step.
  7. On all models, check for battery voltage at terminal No. 10 of ICU plug with ignition on. Voltage should be present with air temperature below 41°F (5°C), and no voltage at higher temperatures. If values are incorrect, check air temperature sensor. See TEST 14  . Replace if faulty. If sensor is okay, repair wiring.
  8. If voltage readings are correct, check for ground at terminal No. 12 of ICU. Connect volt/ohmmeter between terminal No. 12 of plug and ground. Resistance should be zero with throttle closed, and infinite with throttle open. If values are incorrect, check throttle position sensor. See TEST 10  . Replace or adjust as needed. If switch is good, repair wiring.
  9. If resistance values are correct, check ground connection at terminal No. 11 of ICU plug. Connect volt/ohmmeter between terminal No. 11 and ground. Resistance value should be zero. If not, check coolant temperature sensor. See TEST 11  . Replace sensor if faulty. If sensor is good, repair wiring.
  10. If resistance values are correct, and idle control valve is good (Test 5), replace idle control unit.
scientia non olet · About LEMON Manuals