Rheem R802VA07542117MSA Error Code *T088_F: EXV Sensor Measurement Error (Two-Stage Only)

What Does Code *T088_F Mean?

Your two-stage, variable-speed R802VA07542117MSA uses the Bluetooth Communicating IFC (Integrated Furnace Control) to help operate the cooling system's electronic expansion valve (EXV), the valve that meters refrigerant into the cooling coil. The EXV relies on a small set of sensor inputs to calculate superheat and position itself correctly. Code T088_F is logged when those EXV measurements come out inconsistent or outside the expected range, and Rheem lists it as a two-stage-only fault. Rather than pointing at one specific part, T088_F flags that the combined EXV sensing does not add up.

Because the EXV is on the cooling side and not part of combustion, furnace heating is unaffected and the burner runs normally. Rheem rates T088_F as low severity. What can suffer is cooling: if the EXV cannot trust its measurements it may not position itself correctly, so air conditioning performance can drop even though heating stays normal.

T088_F is closely tied to the other two EXV superheat sensors on this board. The suction line temperature thermistor (T085_F) and the suction pressure transducer (T086_F) are the two inputs to the superheat calculation, and T088_F is the code that fires when their combined result is inconsistent, so it can appear on its own or alongside one of those two. This EXV group is separate from the air-temperature sensors (T081_F return, T082_F supply, T084_F outdoor) and from T087_F, the control board's own temperature sensor. All of them are low-severity monitoring faults, not hard lockouts.

Because T088_F describes a measurement inconsistency rather than a single dead sensor, diagnosis often starts by checking the two contributing sensors and their wiring rather than assuming one specific component has failed.

What You'll Notice

• The alphanumeric display shows "T088_F", or the LED blinks the code one digit at a time with a roughly three-second pause between digits
• Heating continues to run normally with no change at the registers
• Air conditioning may cool less effectively or feel weaker than usual
• The fault stays logged in the Bluetooth contractor app after a power cycle
• No lockout occurs, and the effect shows up during cooling operation

Common Causes

How This Is Diagnosed

Because T088_F reports an inconsistency rather than one failed part, a technician evaluates the whole EXV sensing chain: the suction line temperature thermistor, the suction pressure transducer, their wiring back to the control, and the EXV itself. Each sensor's reading is checked against actual measured conditions to see which input is disagreeing with reality.

Connectors are reseated and the harness is inspected for damage, since a wiring fault between a sensor and the control can make otherwise good sensors report conflicting values. If the individual sensors read correctly but the combined measurement is still flagged, the EXV or its control circuit is examined. This is informational only; refrigerant-side work requires refrigeration certification and is not homeowner-safe.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The code stays active and your cooling system is underperforming
• You also see T085_F or T086_F, which point to which contributing sensor may be at fault
• Air conditioning performance has dropped since the code appeared
• The fault clears and returns, suggesting an intermittent connection somewhere in the EXV sensing chain

✓ Verified against manufacturer service manual — March 2026