LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Audi >> 1996 >> Cabriolet >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P1391/17799 - CMP Sensor Short To Ground
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P1391/17799 - CMP Sensor Short To Ground

NOTE: DTC is set when crankshaft position sensor signal is always low with engine speed 50-4000 RPM, with more than 3 crankshaft sensor signals recognized.
  1. Inspect Camshaft Position (CMP) sensor connector for looseness and/or corrosion. CMP sensor is located at rear of left cylinder head. Repair sensor connector as necessary. If sensor connector was not repaired, go to next step. If sensor connector was repaired, erase DTC memory and test drive vehicle.
  2. Turn ignition off. Disconnect Camshaft Position (CMP) sensor 3-pin connector. Turn ignition on. Connect a DVOM between CMP sensor connector terminals No. 1 and 3.
  3. Voltage should be 9 volts. If voltage is within specification, go to next step. If voltage is not to specification, repair open or short in wiring harness between CMP sensor connector and Powertrain Control Module (PCM). See WIRING DIAGRAMS  section. Erase DTC memory and test drive vehicle.
  4. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. Connect VAG 1598/19 test box to PCM wiring harness. Terminal assignments of test box are identical to PCM connectors "A", "B", "C", "D" and "E".
  5. Using DVOM, check resistance between CMP sensor harness connector terminal No. 3 and engine ground. Maximum resistance is one ohm. If resistance is within specification, go to next step. If resistance is not within specification, repair open or short circuit. Erase DTC memory and test drive vehicle. If an open or short circuit cannot be located, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING  in this article.
  6. Using DVOM, check resistance between CMP sensor harness connector terminal No. 1 and test box socket A2. Maximum resistance is one ohm. If resistance is within specification, go to next step. If resistance is not within specification, repair open or short circuit. Erase DTC memory and test drive vehicle. If an open or short circuit cannot be located, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING in this article.
  7. Disconnect 4-pin ignition coil power output stage connector. Ignition coil power output stage is located in right front corner of engine compartment. With CMP sensor connector connected, push back rubber boot on connector. Connect VAG 1527B voltage tester between CMP sensor connector terminals No. 1 and 2. Operate starter for several seconds. Voltage tester should briefly flash every other engine rotation. If voltage tester does not flash as specified, go to next step. If voltage tester flashes as specified, go to step 10).
  8. Turn ignition off. Disconnect CMP sensor 3-pin connector. Using DVOM, check resistance between CMP sensor harness connector terminal No. 2 and test box socket B2. Maximum resistance is one ohm. If resistance is within specification, go to step 10). If resistance is not within specification, repair open or short circuit. Erase DTC memory and test drive vehicle. If an open or short circuit cannot be located, go to next step.
  9. Turn ignition on. Using DVOM, check voltage between test box socket B2 and ground. Voltage should be 4 volts minimum. If voltage is within specification, replace CMP sensor. Erase DTC memory and test drive vehicle. If voltage is not within specification, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING in this article.
  10. Inspect CMP sensor for oil/dirt contamination caused by leaking seal on cylinder head. If CMP sensor is not contaminated, go to next step. If CMP sensor is contaminated, replace seal on cylinder head. Erase DTC memory and test drive vehicle.
  11. Replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING  in this article.
scientia non olet · About LEMON Manuals