Ford 691 Four wheel drive selector fault with incorrect engine speed or vehicle speed

How to read it

Code 691 reads as 6 flashes, pause, 9 flashes, pause, 1 flash on the check-engine light. Jumper the self-test input to signal return at the test connector, then run the key on engine off self test and the running self test, counting the check-engine flashes each time.

What does Ford code 691 mean?

Four wheel drive selector fault with incorrect engine speed or vehicle speed

Common causes of 691

• A four wheel drive selector switch that reports the wrong range
• Worn clutch packs that let engine speed and vehicle speed disagree
• A poor connection or damaged wire in the four wheel drive selector circuit
• A transmission range sensor reading the wrong position

How to fix 691

1. Check the four wheel drive selector switch and its range indication
2. Check the connector pins and wiring in the four wheel drive selector circuit
3. Check the transmission fluid level and condition, and watch for slip under load
4. Test the transmission range sensor and replace it only if it fails its own test
5. Test the PCM last, only after every circuit test has passed
6. Clear the code, then retest to confirm the fix holds

Source

Qualified source review