What Does P0991 Mean?
DTC P0991 indicates the transmission fluid pressure sensor/switch "E" circuit is exhibiting intermittent signal behavior. The TCM is seeing the signal drop out, spike, or fluctuate erratically rather than providing a stable pressure reading. This intermittent condition is often more difficult to diagnose than a permanent fault because the problem may not be present during static testing.
Common Causes
30%
Loose or worn connector terminals at the pressure sensor creating intermittent contact
25%
Cracked or frayed wiring in the sensor harness that makes and breaks contact during vibration
25%
Pressure sensor with an intermittently failing internal element
15%
Corroded connector pins that maintain contact variably depending on temperature and humidity
5%
Intermittent TCM input circuit fault
Diagnostic Steps
1
Monitor the live data for pressure sensor "E" while the vehicle is idling and during a test drive to observe signal dropouts or erratic spikes in real time.
2
Perform a wiggle test at the sensor connector and along the wiring harness while watching the live data; signal disturbances during wiggling pinpoint the fault location.
3
Inspect the sensor connector terminals for spread, corroded, or recessed pins; clean and re-tension terminals as needed.
4
Check for any TSBs related to transmission harness routing or connector sealing issues specific to the vehicle platform.
5
If the connector and wiring test clean, replace the pressure sensor as a likely source of the intermittent signal behavior; drive test to confirm resolution.
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
DTC P0991 indicates the transmission fluid pressure sensor/switch "E" circuit is exhibiting intermittent signal behavior. The TCM is seeing the signal drop out, spike, or fluctuate erratically rather than providing a stable pressure reading. This intermittent condition is often more difficult to dia...
The most common cause of P0991 (Transmission Fluid Pressure Sensor/Switch "E" Circuit Intermittent) is: Loose or worn connector terminals at the pressure sensor creating intermittent contact
Typical repair costs for P0991 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Intermittent pressure feedback can cause the TCM to make erratic shift pressure decisions, leading to unpredictable shift firmness or timing. This inconsistency may catch the driver off guard during acceleration or deceleration maneuvers.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0991 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Generic (SAE)
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