P2799 — Auxiliary Transmission Fluid Pump Control Circuit High #

Please note: The wording of this DTC (Diagnostic Trouble Code) label may vary by manufacturer. Always refer to your service manual or OEM (Original Equipment Manufacturer) resources for precise terminology.

Known label variations:

• Auxiliary Transmission Fluid Pump Control Circuit High (Generic / Multiple OEMs)
• Aux Trans Pump Ctrl Circuit High (Chrysler, Dodge, Jeep)
• Electric Transmission Oil Pump Control High (Toyota, Lexus)
• Auxiliary ATF Pump Circuit High (Honda, Acura)

Summary of code P2799 #

P2799 is an OBD-II trouble code that indicates the Auxiliary Transmission Fluid Pump Control Circuit is reading a voltage that is higher than expected. The auxiliary transmission fluid pump is an electrically powered pump that helps maintain hydraulic pressure in the automatic transmission, particularly during engine stop/start operations or when extra fluid flow is needed. This code is usually detected by the Transmission Control Module (TCM), which monitors the circuit for faults. When the TCM sees a voltage above the specified threshold for a certain period, it triggers code P2799. While it may not cause immediate driveability issues, this code should be addressed to avoid further transmission complications.

Common symptoms for code P2799 #

When code P2799 is present, the vehicle may exhibit subtle or noticeable changes in transmission performance. The auxiliary pump’s malfunction can lead to issues with fluid pressure, affecting gear shifts and overall drivability. Watch out for these symptoms:

• Check Engine Light illuminated
• Transmission warning light or messages on the dashboard
• Harsh or delayed gear shifts
• Transmission stuck in limp mode (reduced performance mode)
• Unusual noises from the transmission area
• Decreased fuel efficiency (in some cases)
• No noticeable symptoms in early or intermittent cases

Most likely causes for code P2799 #

Several potential factors can trigger a high voltage reading in the auxiliary transmission fluid pump control circuit. Here are the most common causes, ranked by frequency:

1. Faulty auxiliary transmission fluid pump (internal electrical short or malfunction)
2. Damaged wiring or connectors in the pump control circuit (corrosion, chafing, or broken wires)
3. Defective pump relay or fuse (if equipped)
4. Failed Transmission Control Module (TCM) (rare)
5. Incorrect voltage supply from the battery or alternator (overcharging condition)
6. Aftermarket modifications or improper repairs affecting circuit integrity

Step-by-step diagnosis for code P2799 #

Proper diagnosis of P2799 involves a systematic approach to identify the root cause. Follow these steps to ensure accuracy and avoid unnecessary part replacement:

• Verify the code using a professional scan tool and check for related transmission codes.
• Inspect the auxiliary pump’s wiring and connectors for signs of corrosion, damage, or loose connections.
• Test the auxiliary transmission fluid pump for resistance and continuity using a digital multimeter (refer to OEM specs).
• Check the pump control relay and fuse (if applicable) for function and integrity.
• Measure voltage at the pump connector with the ignition ON to ensure it matches OEM specifications.
• Monitor the TCM’s command to the pump via live data, confirming that the module is providing correct signals.
• Inspect battery and charging system output for overvoltage conditions.
• Consult OEM service information for any technical service bulletins (TSBs) related to this code.

Possible repairs for code P2799 #

Resolving P2799 depends on pinpointing the exact cause. Here are the most common repairs associated with this code:

• Repair or replace damaged wiring or connectors in the pump circuit
• Replace the auxiliary transmission fluid pump if found faulty
• Replace a defective relay or fuse controlling the auxiliary pump
• Correct battery or charging system overvoltage issues (replace alternator, repair wiring, etc.)
• Reprogram or replace the TCM if diagnosed as faulty (rare)
• Address any aftermarket wiring or modification issues impacting the circuit

Is it safe to drive with code P2799? #

Driving with code P2799 is generally not recommended, especially for extended periods. While some drivers may not notice immediate symptoms, the auxiliary transmission fluid pump plays a crucial role in maintaining proper hydraulic pressure. Ignoring this code could risk transmission overheating, harsh shifts, or even internal damage—especially in heavy traffic or stop/start conditions. If you must drive, do so only to a repair facility and avoid demanding driving situations.

Vehicles most commonly affected by code P2799 #

P2799 appears most frequently on vehicles equipped with advanced automatic transmissions that use an auxiliary or electric fluid pump. While this code can occur on various brands, it is often reported on:

• Toyota and Lexus hybrids and models with stop/start technology
• Chrysler, Dodge, Jeep vehicles with newer 8-speed or 9-speed transmissions
• Honda and Acura automatic transmission models
• Ford and Lincoln vehicles with advanced automatic transmissions
• Some Volkswagen and Audi models with dual-clutch or advanced automatics

Common mistakes and best practices for code P2799 #

Misdiagnosis is common with electrical codes like P2799. To avoid wasted time and money, keep these tips in mind:

• Do not replace the auxiliary pump before thoroughly checking the wiring and relay.
• Always verify the code with a scan tool and check for related codes that may influence diagnosis.
• Use OEM wiring diagrams and service information for accurate troubleshooting.
• Don’t ignore the charging system—high voltage from a faulty alternator can trigger this code.
• Clear codes and retest after each repair step to confirm the fix.

Quick FAQ for code P2799 #

Here are some rapid answers to common questions about P2799:

Q: Will P2799 cause my transmission to fail immediately?
A: Not usually, but driving with a faulty auxiliary pump can accelerate wear or cause overheating, so prompt repair is essential.

Q: Can I reset the code and keep driving?
A: Clearing the code without fixing the root cause will only result in the code returning. Always diagnose and repair the underlying issue.