The Obdii Code P0845 indicates a problem with the Transmission Fluid Pressure (TFP) sensor/switch “B” circuit. This article explains the code, its symptoms, common causes, and diagnostic procedures. Understanding this code is crucial for effective troubleshooting and repair.
What Does the P0845 Code Mean?
The Transmission Fluid Pressure (TFP) sensor/switch, often located on the valve body or transmission case, monitors fluid pressure within the transmission. It converts this mechanical pressure into an electrical signal sent to the Powertrain Control Module (PCM) or Transmission Control Module (TCM). The PCM/TCM uses this signal to determine operating pressure and shift timing, sharing this data with other controllers via the vehicle’s communication network.
The P0845 code specifically points to an issue with the “B” circuit of the TFP sensor. This signifies that the voltage signal received by the PCM/TCM from this circuit deviates from the expected values. This discrepancy can stem from electrical faults within the sensor circuit or mechanical problems within the transmission itself. Consult your vehicle’s specific repair manual to identify the “B” circuit.
Symptoms and Severity of P0845
The severity of a P0845 code varies depending on the affected circuit and the extent of the malfunction. While the PCM/TCM can often compensate for some electrical issues, leading to subtle symptoms, mechanical problems can cause significant drivability concerns.
Common symptoms associated with P0845 include:
- Illuminated Malfunction Indicator Lamp (MIL): The check engine light will typically turn on.
- Shifting Problems: You might experience harsh, delayed, or erratic shifting.
- Limp Mode: The vehicle may enter a “limp mode,” starting in second or third gear to prevent further damage. This is designed to protect the transmission.
Common Causes of P0845
Several factors can trigger a P0845 code:
- Wiring Issues: Open circuits, shorts to voltage, or shorts to ground in the TFP sensor wiring are common culprits. Corrosion or damage to the wiring harness can disrupt the signal.
- Faulty TFP Sensor: A malfunctioning sensor may provide inaccurate readings or no signal at all. This is a frequent cause of P0845.
- Internal Transmission Problems: Mechanical issues like internal fluid leaks, damaged valve body components, low system pressure, or stuck valves can also trigger the code.
- PCM/TCM Failure: While less common, a faulty PCM/TCM can also be responsible, though this usually requires programming after replacement.
Diagnosing and Repairing P0845
Before starting any diagnostic work, consult your vehicle’s Technical Service Bulletins (TSBs) for known issues and solutions related to P0845.
1. Visual Inspection: Begin by locating the TFP sensor and visually inspecting the connector and wiring for damage, corrosion, or loose connections. Clean and apply dielectric grease to the connector terminals as needed.
2. Code Check: After cleaning the connector, clear the codes with a scan tool and see if the P0845 code returns. If not, the connection issue was likely the cause. If the code reappears, further testing is required.
3. Voltage Test: With the key on and engine off, disconnect the TFP sensor connector and measure the voltage at the sensor harness connector using a digital voltmeter (DVOM). Compare your readings to the manufacturer’s specifications. Low or no voltage indicates a wiring or power supply issue.
4. Resistance Test: Using an ohmmeter, measure the resistance of the TFP sensor. Compare your readings to the manufacturer’s specifications. This test helps determine if the sensor itself is faulty. Wiggle the connector while testing to identify intermittent issues.
5. Further Diagnosis: If all previous tests pass and the code persists, suspect a faulty TFP sensor. However, internal transmission problems or a faulty PCM/TCM cannot be ruled out without further specialized testing. Seek professional help if needed.
Remember: Always consult a qualified automotive technician for complex repairs or if you are unsure about any diagnostic steps. Proper diagnosis and repair are crucial for ensuring the safe and reliable operation of your vehicle.
