P077E

What it means

P077E is a generic code meaning the transmission control module has compared readings from more than one transmission fluid temperature sensor and found they do not agree within the expected range. The module cannot be sure which reading is correct, so it sets the fault and may limit transmission functions to protect the gearbox. Which sensors are compared, and how, depends on the model and transmission type.

Symptoms

• Gearbox warning light or engine management light on
• Transmission in limp mode or restricted to certain gears
• Harsh, delayed or flared gear changes
• Torque converter lock-up or cooler control behaving differently
• Gearbox overheating warning or reduced performance when hot
• Fault appears intermittently, often after a cold start or a long drive

Possible causes

• Faulty or drifting transmission fluid temperature sensor, so one reading is out of step with the otherlikely
• Damaged wiring, chafed loom or corroded connector to one of the temperature sensors or the internal harnesslikely
• Incorrect, degraded or contaminated transmission fluid, or the wrong fluid level affecting temperature readingspossible
• Restricted or faulty transmission cooler circuit or thermostatic valve causing real temperature differences between measuring pointspossible
• Fault in the valve body, mechatronic unit or internal sensor assembly (depends on the transmission design)possible
• Transmission control module fault or outdated software where a known issue is documented by the manufacturerrare

How to diagnose

1. Read all stored codes and freeze frame data, noting fluid temperatures, engine coolant temperature and mileage when the code set, and check for related sensor circuit codes
2. Check the transmission fluid level and condition, and confirm the correct fluid specification has been used for that model
3. Inspect the wiring, connectors and any external sensor plugs for damage, corrosion, water ingress or heat damage
4. Compare live data from each fluid temperature sensor on a cold car after it has stood overnight; readings should be close to ambient and to each other
5. Monitor the readings during a warm-up drive and see which sensor deviates, and whether it jumps, freezes or drifts
6. Check the cooler lines and thermostatic valve for blockage or poor flow, following the procedure for that transmission
7. Test the sensor circuits for resistance, voltage and continuity against the manufacturer's data for the model
8. Check for applicable manufacturer service bulletins or software updates for the transmission control module

How to fix

• Replace the faulty temperature sensor or the sensor assembly that contains it, as the model requires
• Repair or replace damaged wiring and connectors, and clean or reseat terminals
• Correct the fluid level, or change the fluid and filter using the correct specification if it is degraded or contaminated
• Clear any restriction in the transmission cooler circuit or replace a faulty cooler or valve
• Replace the valve body, mechatronic unit or control module if testing proves it faulty, and apply any approved software update where an outdated calibration is a known cause

Can I keep driving?

Nearby codes

• P077DGenericOutput Shaft Speed Sensor Circuit High
• P077FGenericReverse 2 Incorrect Ratio