This case report concerns the diagnosis of a Volvo V50 (2008 model, left hand drive) with a single rear parking assistance sensor malfunction.
Presenting symptoms
- Dashboard message warning of parking assistance system failure
- Persistent PAM-0007 diagnostic trouble code (DTC) (parking sensor 3 Signal too low/Signal missing). The DTC is triggered when module is powered up (Key-On, Engine-Off) and does not require the transmission to be in reverse.
Background
The V50 has 4 bumper mounted ultrasonic proximity sensors which sound an alarm when a reversing car comes near an obstruction. In left hand drive cars, the rear parking sensors are numbered starting at the left (driver’s) side. Sensor 3 is therefore third from the left (or “rear right inside”).
Diagnosis
Preparation
Remove the back plastic bumper by unscrewing 2 torx bolts at the back of the bumper and the torx screws in the rear wheel wheel attaching the bumper to the wheel well shield. Pull the bumper up and away with care not to strain the wire harness on the right hand side. To free the bumper, disconnect the harness 6-pin connector
The basics – Inspect and clean all wiring and connectors
I. Is sensor 3 (7/133, third from left) functional?
Test: Clear trouble codes, switch the suspected sensor with another sensor (mark it first to avoid confusion!), re-scan and see if the Diagnostic Trouble Code (DTC) “changes positions”. To remove the sensor, first disconnect its electrical connector and the push back the 2 locking tabs and pull the sensor straight upwards. A tab on the sensor will prevent twisting at first. It will be helpful to lubricate the sensor holder with silicone spray.
II. Is the signal wire between sensor 3 and cable harness connector 64/53 broken or shorted to ground or power?
Test: With the bumper disconnected from the car’s harness, check continuity between:
- Sensor pin 2 and Connector pin 3 (expect continuity)
- Sensor pin 2 and Connector pin 1 (expect no continuity)
- Sensor pin 2 and Connector pin 6 (expect no continuity
(note: for other sensors, signal wires will terminate in Connector pins 2, 4, or 5 see schematic)
III. Does the fault exist between the Parking Assist Module (PAM) and connector 64/53?
Test: Repeat step 2 from the PAM