TECH TIP
Ford Focus Brake Lamps Cause Transmission Problems
Feb. 02 2021
Feb. 02 2021

Vehicle:  2005 Ford Focus, L4-2.0L, VIN N, Automatic Transmission

Mileage: 221,093

Problem: This Ford Focus, equipped with the 4F27E transmission, arrived at a transmission specialty shop with an inoperative third gear.

Case Details: The shop rebuilt the transmission and the car drove fine after the repairs. Not long after, however, the vehicle returned with a “default-in-third-gear" concern. After connecting a scan tool and looking at the live parameter identification data (PID), the technician discovered that when the transmission was shifted into 2nd or 1st, the PID indicated that the transmission was still in 3rd gear. When shifted into Drive, the PID indicated that the transmission was in 2nd gear.

The technician also retrieved the following diagnostic trouble codes (DTCs) from the powertrain control module (PCM):

  • P0705 Transmission Range Sensor
  • P1702 Transmission Range Sensor Intermittent

The technician replaced the Transmission Range (TR) Sensor, but that didn’t fix the problem.

A call to ALLDATA Tech-Assist for some advice really helped solve this mystery. The Tech-Assist consultant advised the technician that in Ford’s transmission range (TR) sensor diagnostic Pinpoint Test C, there is a precaution that states that DTC P0705 may also be set because of an open ground in the tail lamp circuit. It advised to check the tail lamps for opens or poor grounds and repair the tail lamp circuit as necessary.

Confirmed Repair: Rather than the tail lamps being the cause, the technician discovered that only one of the high-mounted brake lamp bulbs ("third brake lamp") in the strip of six was working. He replaced all the third brake lamp bulbs. Afterwards, the “default-in-third-gear" concern vanished, no DTCs returned and the MIL stayed off. Problem solved!

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