Input/Turbine Speed Sensor "A"/"B" Correlation

Possible causes

• CommonFailed speed sensor
• CommonCorroded connector or wiring damage at the sensor
• CommonMetal debris on the sensor tip, from internal wear
• PossibleDamaged or contaminated reluctor ring
• PossibleInternal transmission harness failure
• PossibleSlipping clutch, so the speeds really are wrong

What you might notice

• Transmission stuck in one gear
• Harsh or erratic shifting
• Slipping - engine speed rising without matching acceleration
• Speedometer erratic on some vehicles
• Check engine light on

What to check, in order

1. Watch both sensors together on the live data screen. The one that does not track the other is the fault.
2. Check whether the transmission is genuinely slipping. If the speeds really do differ, both sensors may be right and the transmission is at fault.
3. Watch the speed readings on the live data screen while driving. Input, intermediate and output speeds should track each other in a fixed ratio in each gear.
4. Inspect the sensor tip for a coating of metal filings. Debris here is not just the fault - it is evidence of internal wear that will need addressing.
5. Check the connector and wiring for corrosion and chafing.
6. Check the fluid level and condition first. It is the cheapest check and it explains more transmission complaints than every electrical fault combined.
7. Where the sensor is internal, eliminate the external wiring and the case connector before dropping the pan.