P2799 — Auxiliary Transmission Fluid Pump Control Circuit High

OBD2 code P2799 flags a problem with the automatic transmission control (auxiliary transmission fluid pump control circuit high). Short, gentle driving to a shop is usually possible. Common culprits: internal mechanical wear (clutches, torque converter), wiring or connector faults in the valve body harness, faulty transmission speed sensor.

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm P2799 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
  4. Subsystem check With the auxiliary transmission fluid pump control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
  5. Subsystem check Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
  6. Subsystem check Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
  7. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2799 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2799 (parts and labor, USD, independent shop rates): Replace a shift solenoid: $300–$800; Transmission fluid service: $150–$350; Transmission rebuild or replacement: $2,500–$5,500; Valve body repair or replacement: $700–$1,500. Overall, fixing P2799 usually costs between $150 and $5,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What are the symptoms of P2799?

Drivers most often notice: transmission stuck in one gear (limp mode), Check Engine or transmission warning light on, slipping between gears, harsh or delayed shifting.

What does OBD2 code P2799 mean?

OBD2 code P2799 flags a problem with the automatic transmission control (auxiliary transmission fluid pump control circuit high). Short, gentle driving to a shop is usually possible. Common culprits: internal mechanical wear (clutches, torque converter), wiring or connector faults in the valve body harness, faulty transmission speed sensor.

Is it safe to drive with P2799?

Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

How much does it cost to fix P2799?

Replace a shift solenoid — $300–$800; Transmission fluid service — $150–$350; Transmission rebuild or replacement — $2,500–$5,500; Valve body repair or replacement — $700–$1,500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

How do I diagnose P2799 myself?

Start with a scan: confirm P2799, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the auxiliary transmission fluid pump control, and verify the suspect component against live data before buying parts.

What does P2799 mean?

P2799 is logged by the onboard diagnostics when the automatic transmission control does not behave as expected. The official definition is “Auxiliary Transmission Fluid Pump Control Circuit High”. This is a powertrain (engine/transmission) category code.

“Circuit high” means the control module sees a voltage on the auxiliary transmission fluid pump control circuit that is above the expected range — typically close to battery voltage. Physically this points to a short to a power feed, a broken ground return, or a failed component pulling the signal line high.

To set P2799, the control module compares live readings of the automatic transmission control against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

Common symptoms of P2799

  • transmission stuck in one gear (limp mode)
  • Check Engine or transmission warning light on
  • slipping between gears
  • harsh or delayed shifting
  • shuddering at highway speed
  • no movement in severe cases

What causes P2799?

  • open ground return of the auxiliary transmission fluid pump control
  • signal wire shorted to battery positive
  • failed auxiliary transmission fluid pump control pulling the signal high
  • wiring or connector faults in the valve body harness
  • faulty transmission speed sensor
  • failed shift or pressure control solenoid
  • internal mechanical wear (clutches, torque converter)

How to diagnose P2799

  1. Connect an OBD2 scanner, confirm P2799 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
  4. With the auxiliary transmission fluid pump control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
  5. Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
  6. Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
  7. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2799 does not return.

How to fix P2799

Start with the cheapest and most common causes before replacing expensive parts:

  • Replace a shift solenoid — $300–$800
  • Transmission fluid service — $150–$350
  • Transmission rebuild or replacement — $2,500–$5,500
  • Valve body repair or replacement — $700–$1,500

How much does it cost to fix P2799?

Repair cost depends on which component actually failed. Typical scenarios for P2799 (parts and labor, USD, independent shop rates):

  • Replace a shift solenoid: $300–$800
  • Transmission fluid service: $150–$350
  • Transmission rebuild or replacement: $2,500–$5,500
  • Valve body repair or replacement: $700–$1,500

Overall, fixing P2799 usually costs between $150 and $5,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P2799?

Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

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