Error Code P0845 is defined as Transmission Fluid Pressure Sensor / Switch B Circuit. Error Code P0845 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present. This includes vehicles from, but not limited to, Chrysler, Chevrolet, Dodge, GMC, Honda, Nissan, and Toyota. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.
The TFPS or Transmission Fluid Pressure Sensor/Switch is usually attached to the valve’s side inside the transmission. In some cases, it’s screwed to the side of the transmission case/body itself.
The job of the TFPS is to convert mechanical transmission into an electrical signal for the PCM (powertrain control module) or TCM (transmission control module). Usually, the PCM/TCM will inform the other controllers using the vehicle’s data communication bus.
The PCM/TCM gets the voltage signal to determine the operating pressure of the transmission, or when a shift is happening. This Error Code is set if the “B” input is unable to match the normal operating voltages stored in the memory of the PCM/TCM. Internal mechanical issues in the transmission can also cause this code. It’s best to refer to the vehicle’s specific repair manual to pinpoint the “B” circuit of a particular vehicle.
Error Code P0845 is usually an electrical circuit (TFPS sensor circuit) problem. However, it can also be caused by mechanical problems such as cracked or missing check balls in the valve body, internal leaks, stuck valve in the valve body, or low system operating pressure/mainline pressure. It’s important not to overlook these factors in the troubleshooting stage, especially if the problem is intermittent.
The steps for troubleshooting may vary from one manufacturer to another, wire colors, and TFPS sensor type.
Other related TFPS B circuit codes include:
- Change in shift quality (loss of shifting ability, lack of engagement or disengagement from torque converter clutch)
- Harsh shifting
- Slipping transmission
- Overheated transmission
- Increase in fuel consumption
- Vehicle starts in second or third gear (limp mode)
- Blocked transmission fluid passages
- Mechanical failure of the transmission
- Open in the signal circuit to TFPS sensor
- Short to voltage in the signal circuit to TFPS sensor
- Short to ground in the signal circuit to TFPS sensor
- Failed TFPS sensor (likely caused by internal mechanical transmission problem)
- Failed PCM (rare, replacement will require reprogramming)
How to Check
As with most codes, you will need a source of vehicle-specific diagnostic information, a diagnostic scanner, and a DVOM (digital volt/ohmmeter) to properly diagnose this error code.
Try to look for any power related codes set along with Error Code P0845, or if there’s a more than one pressure sensor/switch code set. If there is, start your diagnosis with the power-related error code first, or with the multiple code diagnosis first, as this could be a reason behind the error code.
Next, locate the vehicle’s TFPS. It’s usually attached to the side valve of the body inside the transmission or screwed into the side of the transmission case/body itself. Then, inspect the connectors and wirings. Look for any signs of damage, such as bare wires, burnt spots, rubbing, scraping, melted plastic, etc. Carefully inspect each terminal (metal parts) inside the connector by pulling the connectors. Look for signs of burn or corrosion (green tint). This is especially true if they’re attached outside the transmission case. You can use an electrical contact cleaner and a plastic bristle brush to clean the terminals. Let it dry before applying electrical grease where the terminals contact.
Next, clear the diagnostic trouble codes from memory using a scan tool. See if the code returns. If the code doesn’t return, then the problem is likely in the connection. This is common for this code as the external transmission connection is highly susceptible to corrosion.
If the Error Code returns, you will need to test the TFPS sensor and its associated circuits. With Key Off, disconnect all electrical connectors at the TFPS sensor. Then, connect your DVOM’s (digital voltmeter) black lead to the ground or low reference terminal at the TFPS sensor wiring harness connector. Then, connect the red lead of the DVOM to the signal terminal at the TFPS sensor wiring harness connector. Next, turn the Key On Engine Off. The voltmeter should be at either 12V or 5V (check with the manufacturer’s specifications. Try to wiggle the connections to see if they change. If the DVOM shows incorrect voltage, then repair the power or ground wire. You may also need to replace the PCM/TCM.
If it passed the previous test, connect one lead of the DVOM to the signal terminal at the TFPS sensor and the other lead to the ground, or low reference terminal at the sensor. Check with the manufacturer’s specification for the resistance of the sensor to test the resistance pressure. This is especially important to test the resistance to pressure accurately when there is no pressure applied to it. Next, wiggle the connector at the TFPS sensor/switch while monitoring the resistance. If it’s unable to pass, then you will need to replace the TFPS.
If the vehicle passes in all tests mentioned above and the code persists, you likely have a failed TFPS sensor. Failed PCM/TCM or internal transmission malfunction (until the TFPS sensor is replaced) can’t be ruled out.
If you’re unsure what to do up to this point, then it’s best to take the vehicle to a licensed technician for a thorough diagnosis and repair.
How to Fix
- Cleaning of dirty connectors at the TFPS connector
- Repair or replacement of damaged wires and connectors
- Replacement of pressure control solenoid
- Refilling or flushing, and replacement of old transmission fluid
- Clearing the blocked transmission fluid passages
- Replacement of faulty TFPS
- Replacement of PCM/TCM
To install the PCM/TCM correctly, it must be programmed or calibrated to the vehicle.
The severity of the symptoms and problems depends on which circuit the failure took place. For an electrical failure, the PCM/TCM can compensate to some degree. This failure means the PCM/TCM modifies the shifting of the transmission is electronically controlled.