Diagnostic trouble code (DTC) P0847 indicates a "Transmission Fluid Pressure Sensor/Switch 'B' Circuit Low" issue. This code is specifically logged by the powertrain control module (PCM) when it detects a problem within the hydraulic clutch system or with the pressure switch itself.
This code signals that the PCM is receiving an abnormally low voltage reading from the 'B' circuit of the transmission fluid pressure sensor or switch. This circuit is crucial for monitoring the fluid pressure within the transmission, which is vital for proper gear engagement and operation.
Understanding P0847
The presence of the P0847 code suggests that there is an electrical or mechanical fault preventing the transmission fluid pressure sensor or switch from reporting accurate pressure readings to the PCM.
- Diagnostic Trouble Code (DTC): P0847 falls under the "P" series of codes, which relate to powertrain issues, specifically the transmission in this case.
- Transmission Fluid Pressure Sensor/Switch 'B' Circuit: Modern automatic transmissions rely on fluid pressure to operate the clutches and bands that engage different gears. Sensors and switches monitor these pressures to ensure smooth and correct gear changes. The 'B' circuit refers to a specific part of this system, indicating where the low voltage reading is detected.
- Circuit Low: This typically means the PCM is receiving a voltage signal that is below the expected operational range for that circuit. This could be due to a faulty sensor, a wiring issue (short to ground, open circuit), or a problem with the hydraulic system itself.
Common Implications of P0847
While the code itself points to a circuit issue, the underlying problem can affect various aspects of transmission performance.
- Gear Shifting Problems: Incorrect pressure readings can lead to harsh shifts, delayed shifts, or the transmission getting stuck in a particular gear (limp mode).
- Reduced Fuel Economy: Inefficient transmission operation can lead to increased fuel consumption.
- Dashboard Warning Lights: The Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) will typically illuminate when this code is set.
Key Aspects of Code P0847
| Aspect | Description |
|---|---|
| Code Meaning | Transmission Fluid Pressure Sensor/Switch 'B' Circuit Low |
| Code Type | Diagnostic Trouble Code (DTC) |
| Triggering Module | Powertrain Control Module (PCM) |
| Potential Problem Areas | Hydraulic clutch system, Transmission Fluid Pressure Sensor/Switch 'B' (electrical or mechanical fault) |
| Indicated Fault | Low voltage reading from the specified circuit, below the manufacturer's specified range. |
What Causes Code P0847?
The "circuit low" nature of P0847 often points to electrical issues, but it's crucial to consider the entire system. Common causes include:
- Faulty Transmission Fluid Pressure Sensor/Switch: The sensor or switch itself may be defective and unable to provide accurate voltage signals.
- Wiring Problems:
- Short to Ground: The wiring for the 'B' circuit might be shorting to ground, causing the voltage to drop.
- Open Circuit: A break in the wiring or a loose connection can prevent the voltage signal from reaching the PCM.
- Corroded Connectors: Corrosion on the sensor or PCM connectors can impede proper signal transmission.
- Low Transmission Fluid Level: While less direct, extremely low fluid levels can sometimes cause unusual pressure readings or affect sensor operation.
- Internal Transmission Issues: In some cases, internal hydraulic problems within the transmission (like a failing hydraulic clutch or valve body issue) can lead to pressure abnormalities that are then detected by the sensor, leading to the code being set.
- PCM Issues: Though less common, a faulty powertrain control module could misinterpret signals or fail to process them correctly, leading to a false P0847 code.
