Fix P0846: Mechanic’s solutions that WORKED

The P0846: Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance indicates an issue with the Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit, which is part of the system monitoring the transmission’s hydraulic pressure. This sensor informs the vehicle’s Transmission Control Module (TCM) about the hydraulic pressure in parts of the transmission, and if the readings are out of the expected range or performance, it triggers this fault code.

P0846 quick overview

Meaning	P0846: Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance
Is it serious?	This code can be serious as it relates to the transmission’s performance and could lead to more significant issues if not addressed.
Possible causes	– Faulty transmission fluid pressure sensor/switch – Damaged or corroded wiring and connectors in the transmission fluid pressure circuit – Contaminated or low transmission fluid – Internal transmission hydraulic faults – Malfunctioning Transmission Control Module (TCM)
How to diagnose?	Check Fluid Levels and Quality: Ensure the transmission fluid is at the correct level and in good condition. Inspect Wiring and Connectors: Examine the transmission fluid pressure sensor/switch wiring and connectors for any signs of damage or corrosion. Test Sensor/Switch Functionality: Use a diagnostic tool or multimeter to test the transmission fluid pressure sensor/switch operation. Monitor Pressure Sensor Data: If possible, use a scan tool to observe the pressure sensor data and compare it to the manufacturer’s specifications. Inspect Transmission Internally: Consider internal transmission inspection if external checks do not reveal any issues.

How to fix P0846 – learn from mechanics

I looked into P0846 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Dodge

Vehicle Information: 2010 Dodge Grand Caravan SXT 3.8L

Issue + Repair History: Came in with check engine light on, safe mode, and code P0750 related to the solenoid L/R circuit. Replaced the solenoid pack but then encountered code P0846 and safe mode again.

Other OBD2 Codes + Test Results:

• P0750: Solenoid L/R circuit issue
• P0846: New code after solenoid pack replacement

Suggestions to Fix Issue:

• Check for voltage on the 2/4 pressure switch line (yellow/dark green) and ensure it is not shorted to power or ground.
• Verify if the solenoid pack is defective.
• Examine the gasket under the pack for correct placement.
• Inspect the connector at the transmission for issues.
• Evaluate possible wiring issues from the computer, such as pinched or rubbed through wires on the case.
• Use scan tool to monitor 2nd and 4th gear pressure switches and gear selection.

Final Fix: The issue was resolved after rechecking the solenoid pack and finding a loose connection inside. Reassembled correctly, addressing the internal connection issue.

Case #2: Jeep

Vehicle Information: 2008 Jeep Grand Cherokee Limited 5.7L

Issue + Repair History:

• Experienced hard shifting to 4th gear and check engine light came on.
• Initially set a P0846 code (Transmission Fluid Pressure Sensor / Switch B Circuit Range Performance).
• Replaced the transmission fluid pressure sensor.
• Later set a P0846 2-4 or 2c pressure switch rationality code, triggered mostly after shifting to 2nd gear.

Other OBD2 Codes + Test Results:

• P0846: 2-4 OR 2C Pressure Switch Rationality

Suggestions to Fix Issue:

• Consider the possibility of a known issue with the 545rfe solenoid pack in these transmissions.
• Check for the 2C 4C clutch bulkhead snap ring potentially being dislodged.
• Explore hydraulic/mechanical issues inside the transmission.
• Investigate the Transgo shift kit as it has an upgraded snap ring and a detailed diagram of the drum and clutch setup.

Final Fix:

• Found that the 2C clutch pressure switch circuit sent 12V back to the PCM when there was no hydraulic pressure. Discovered momentary voltage dropouts while back-probing at the PCM with KOEO, which were influenced by moving the shifter.
• Determined the issue was with an open or shorted to ground 2C clutch switch circuit, likely causing a short to ground that pulled down the 12V. Found the harness rubbed through on top of the transmission under the shifter cable, which was repaired to resolve the issue.

Case #3: Dodge

Vehicle Information: 2004 Dodge Ram 1500 ST 4.7L

Issue + Repair History:

• Transmission intermittently operated properly, sometimes going into limp mode (stuck in 2nd or 3rd gear).
• Initial diagnostic trouble code: P0846 (2c switch circuit).
• After replacement of the PCM/TCM, the problem persisted.
• Applied 12V jump to pin 85 (relay) which temporarily resolved the issue.
• Checked for open/shorted wires at PCM pin 16 to pin 85, which tested OK.
• Updated issue: P0846 code resolved, but now facing intermittent operation and a new code P0750.

Other OBD2 Codes + Test Results:

• P0846: Transmission fluid pressure sensor/switch “B” circuit range/performance
• P0755: Shift Solenoid “B” Malfunction (initially thought to be P0750)

Suggestions to Fix Issue:

• Check TCM relay and connections.
• Consider issues with the valve body or solenoid pack.
• Look into wiring issues, especially near the TCM connector.
• Examine the possibility of an internal hydraulic or mechanical fault in the transmission.

Final Fix:

• Found excessive amp draw from the transmission solenoid pack on L/R Solenoid.
• Measured 1.2 ohms and amp draw of 9.9 amps when loading circuit (normal draw is 6.5A at 1.5ohms).
• Identified the issue to be with the transmission solenoid pack, leading to its replacement.
• Resolved the P0846 code and corrected the intermittent transmission operation.

Case #4: Dodge

Vehicle Information: 2004 Dodge Neon SXT 2.0L

Issue + Repair History:

• Throwing codes P0846 and P0755.
• Initially, the vehicle rarely went into first gear when selecting drive.
• After clearing the codes and putting it in drive, it would select first gear but then stall out, seemingly locking up the transmission.
• After stalling, it would be stuck in second gear with the two codes reappearing.
• Replaced the solenoid pack as initial tests pointed to it being bad, but issue persisted.
• All circuits tested and followed diagnostic procedures according to Mitchell.
• Tried swapping the new solenoid pack with a known good used one.

Other OBD2 Codes + Test Results:

• P0846: 2-4 Pressure Circuit.
• P0755: 2-4 Solenoid Circuit.

Suggestions to Fix Issue:

• Check for a stuck valve in the valve body; consider replacing or repairing the valve body.
• Replace input/output speed sensors as well.
• Ensure code descriptions are accurate for targeted diagnostics.
• Consider possible causes like a faulty TCM or wiring harness issues.
• Probe harness from TCM end with a tail light bulb to energize solenoids; avoid using a test light.
• Check PCM build date; replace PCM if within certain date ranges indicating internal driver failure.

Final Fix:

• After extensive diagnostics and testing, discovered that the 2-4 solenoid would read open/close very fast, then the vehicle would die and get stuck in second gear.
• Replaced the computer and immobilizer from another car.
• This resolved the issue; vehicle now shifts normally with no more codes.

Case #5: GMC

Vehicle Information: 2004 GMC Sierra 2500 HD SLE 8.1L

Issue + Repair History:

• Code P0846 indicating solenoid sticking open.
• Transmission was removed 3 weeks prior for rear main seal replacement.

Other OBD2 Codes + Test Results:

• P0846 – Solenoid sticking open.

Suggestions to Fix Issue:

• Check the connector at the transmission for any bent pins or pinched wires. Ensure the wire loom is not pinched between the engine and transmission.
• Inspect the wiring harness thoroughly for any damage or pinching.
• Monitor the Transmission Fluid Pressure (TFP) switch B with a scan tool. Check its state with the key on engine off, then when the engine is started, and while shifting into drive and reverse.
• If the switch is stuck, check for 12V reference voltage at the transmission connector. If voltage is present, consider removing the transmission pan and TFP switch for further inspection.
• Test the TFP switch manually with a pencil eraser tip while monitoring with a scan tool and grounding the switch.
• Check the transmission fluid level, as low fluid can cause this issue. If the fluid level is not low, continue diagnosing the TFP switch D, not the shift solenoids.

Final Fix:

• Replaced the solenoid due to an internal short.

Takeaway Advice	Description of Diagnostic Step
Check Transmission Fluid Level and Quality	Ensure the transmission fluid is at the correct level and is not contaminated or degraded.
Inspect Wiring and Connectors	Examine all related wiring and connectors for damage, corrosion, or loose connections.
Replace Solenoid Pack (if applicable)	If diagnostics point towards a faulty solenoid pack, consider its replacement.
Test Pressure Sensor/Switch	Use specialized tools to test the pressure sensor/switch for proper operation.