P0991 code meaning
Transmission Fluid Pressure Sensor/Switch E Circuit Intermittent
What P0991 means
The module has seen the signal of the fifth transmission pressure sensor or switch drop out or jump briefly, without a steady low or high reading. No manufacturer documents this code publicly. The only switch E found in public sources is GM's TFP switch 5 in the 6T70/6T75 valve body module (Saab 9-4X 2011), a normally closed switch that GM monitors only through P0989 and P0990: signal stuck low at commanded pressure of 50 kPa or less, or stuck high, counted over clutch releases and logged as Special No Trip without MIL. An intermittent check would follow the CARB rule that transmission inputs be monitored for circuit faults. Steady faults are P0987 to P0990. Expect frozen shift adaptation and the odd harsh shift.
P0991 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0991
- Stored fault, often without warning light
- Occasional harsh or flared shift
- Shift adaptation frozen
Common causes of P0991
- Most likelyLoose or corroded contact at the valve body module connector
- PossibleDebris or damaged diaphragm film making the switch contact flicker
- PossibleChafed internal harness that shorts or opens under vibration
- Less likelyFault in the transmission control module input stage
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Tfp sensor eWiring harnessTCM
What each part of P0991 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9 | Area: transmission. |
| 91 | The exact fault in that area. |
What to do next
- Note P0991 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0991
What does P0991 mean?
P0991 means "Transmission Fluid Pressure Sensor/Switch E Circuit Intermittent". The module has seen the signal of the fifth transmission pressure sensor or switch drop out or jump briefly, without a steady low or high reading. It is a generic code, so it means the same on every make.
Is it safe to drive with P0991?
P0991 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0991 fail an emissions test?
P0991 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0991 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P0991 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.