What Does P2798 Mean?
The voltage in the auxiliary transmission fluid pump control circuit is below the expected range. This low voltage prevents the TCM from properly commanding pump operation.
Common Causes
30%
Poor ground connection at auxiliary pump motor or control circuit
25%
High resistance in power supply circuit due to corroded connections
20%
Partially failed pump motor with internal resistance creating voltage drop
15%
Damaged or undersized wiring causing excessive voltage drop
10%
Weak battery or charging system issue reducing available voltage
Diagnostic Steps
1
Step 1: Test battery voltage and charging system (minimum 12.4V at rest, 13.8-14.5V running)
2
Step 2: Measure voltage at pump connector during operation; should be within 1V of battery voltage
3
Step 3: Test ground circuit resistance from pump ground to battery negative (should be less than 0.5 ohms)
4
Step 4: Perform voltage drop test on power supply circuit under pump load
5
Step 5: Measure pump motor current draw and compare to specifications to identify excessive resistance
Estimated Repair Cost
$150 - $1,400
Parts + labor, varies by vehicle and location
The voltage in the auxiliary transmission fluid pump control circuit is below the expected range. This low voltage prevents the TCM from properly commanding pump operation.
The most common cause of P2798 (Auxiliary Transmission Fluid Pump Control Circuit Low) is: Poor ground connection at auxiliary pump motor or control circuit
Typical repair costs for P2798 range from $150 to $1,400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Insufficient transmission fluid circulation can cause overheating and premature transmission failure. Avoid prolonged idling and heavy traffic conditions until diagnosed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2798 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Lubrication System
Difficulty
Type
Generic (SAE)
Recommended Tools
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