P2798 — Auxiliary Transmission Fluid Pump Control Circuit Low

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

Read the code and freeze frame Connect an OBD2 scanner, confirm P2798 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
Subsystem check Check for supply voltage at the auxiliary transmission fluid pump control connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Subsystem check Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
Subsystem check Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2798 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2798 (parts and labor, USD, independent shop rates): Replace a shift solenoid: $300–$800; Transmission rebuild or replacement: $2,500–$5,500; Valve body repair or replacement: $700–$1,500; Transmission fluid service: $150–$350. Overall, fixing P2798 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 does OBD2 code P2798 mean?

Auxiliary Transmission Fluid Pump Control Circuit Low (P2798): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by failed shift or pressure control solenoid, internal mechanical wear (clutches, torque converter), low or degraded transmission fluid.

Is it safe to drive with P2798?

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.

What are the symptoms of P2798?

Drivers most often notice: transmission stuck in one gear (limp mode), slipping between gears, no movement in severe cases, Check Engine or transmission warning light on.

What is the most common cause of P2798?

The most common causes are: failed shift or pressure control solenoid, internal mechanical wear (clutches, torque converter), low or degraded transmission fluid.

Will P2798 clear itself?

Sometimes P2798 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does P2798 mean?

The engine control module sets P2798 when it detects a fault in the automatic transmission control. In practical terms: auxiliary transmission fluid pump control circuit low. The code belongs to the powertrain (engine/transmission) group of OBD2 codes.

“Circuit low” means the voltage on the auxiliary transmission fluid pump control circuit stays below the expected minimum — close to ground. The usual physical reasons are a short to ground, a chafed wire touching metal, a missing supply voltage, or a failed component dragging the signal down.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores P2798 and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

Common symptoms of P2798

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

What causes P2798?

missing supply voltage to the auxiliary transmission fluid pump control
signal wire shorted to ground (chafed insulation)
failed auxiliary transmission fluid pump control pulling the signal low
low or degraded transmission fluid
valve body wear
faulty transmission speed sensor
failed shift or pressure control solenoid
wiring or connector faults in the valve body harness

How to diagnose P2798

Connect an OBD2 scanner, confirm P2798 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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.
Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
Check for supply voltage at the auxiliary transmission fluid pump control connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2798 does not return.

How to fix P2798

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

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

How much does it cost to fix P2798?

Repair cost depends on which component actually failed. Typical scenarios for P2798 (parts and labor, USD, independent shop rates):

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

Overall, fixing P2798 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 P2798?