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Home / DTC / P2798 — Electric/Auxiliary Transmission Fluid Pump A Control Circuit Low

P2798 — Electric/Auxiliary Transmission Fluid Pump A Control Circuit Low

Detailed page for trouble code P2798.

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Code

P2798

Generic P — Powertrain

Electric/Auxiliary Transmission Fluid Pump A Control Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 13 EN: 22 RU: 15
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Page language: EN

Causes

  • Blown fuse or tripped circuit breaker in pump power feed
  • Faulty pump (open/shorted motor or internal failure)
  • Damaged wiring harness (open circuit, corrosion, chafing) or poor connector pin contact
  • Short to ground on the pump control or power circuit
  • Faulty relay or driver in the power/ground feed to the pump
  • Defective PCM/TCM or pump driver output

Symptoms

  • Transmission auxiliary pump does not run when commanded
  • Transmission warm-up or pressure delays, possible shift complaints
  • DTC P2798 stored, MIL (check engine/transmission lamp) may be illuminated
  • Intermittent pump operation or loss of pump function under load
  • Possible unusual noise or no noise from pump when it should run

What to check

  • Read freeze frame and freeze data; note conditions when code set
  • Check battery voltage (key on/engine off and when cranking) and charging system health
  • Inspect fuses and relays related to transmission pump and replace if blown
  • Visually inspect pump connector and harness for corrosion, bent pins, damage or water intrusion
  • Use a scan tool to command the pump ON and observe status/feedback and any active tests
  • Measure voltage at pump connector (supply and control) with command ON and OFF

Signal parameters

  • Supply voltage at pump connector (expected): ~11–14.5 V with engine running or key on when pump commanded
  • Control/driver output: when commanded ON should present drive voltage or PWM (varies by design); when OFF should be ~0 V or open
  • Pump motor resistance (typical passenger vehicles): low ohms range — if reading is infinite or very high, motor is open; if near 0 Ω, suspect short
  • Pump running current: can be several amps (often 2–20 A depending on design) — abnormally high or low current indicates motor or load issue
  • Diagnostic thresholds: controller registers 'low' when command expected voltage is absent or below manufacturer threshold

Diagnostic algorithm

  1. Retrieve and record freeze frame data and any related codes. Confirm P2798 is current and note operating conditions when it set.
  2. Visually inspect pump area, connectors and wiring for damage, corrosion, water intrusion, or loose pins. Repair any obvious issues and clear codes to retest.
  3. Verify battery and charging system voltage. Low battery/charging faults can cause low-circuit detections; correct if necessary.
  4. Check fuses and relays for the pump circuit; replace faulty items and recheck. Some vehicles use a separate relay or TCM-controlled relay.
  5. Using a scan tool, command the auxiliary pump ON while monitoring requested/actual status. Listen for pump operation and note any reaction.
  6. With connector disconnected and vehicle safe, measure supply voltage at pump power pin with pump commanded ON. Expect battery voltage. If absent, trace back to fuse/relay/connection.
  7. Measure the control/driver pin voltage at the pump connector during commanded ON. If the control is low when it should be high (or vice versa depending on design), suspect wiring or module driver issue.
  8. Check continuity between the pump connector and the PCM/TCM pin. Repair any open or high-resistance circuits. Also check for shorts to ground or battery.
  9. Reconnect connector and perform a current draw test while commanding pump ON. Compare to expected draw. Low or zero current suggests open motor or open wiring; very high current indicates internal motor fault or mechanical jam.
  10. If wiring, fuses and pump bench tests are good, consider replacement of the pump driver or PCM/TCM diagnostic and repair per manufacturer guidance. Reprogram/relearn if required.
  11. After repairs, clear codes and perform road/operational test to confirm code does not return and pump operates correctly.

Likely causes

  • Broken or corroded connector at pump (most common)
  • Open fuse or bad relay supplying pump
  • Failed pump motor (does not draw expected current)
  • PCM/TCM output driver fault (less common)

Fault status

⚠️ Status
Controller detected low voltage on Electric/Auxiliary Transmission Fluid Pump A control circuit. Possible open/short, failed pump, blown fuse/relay, or module driver fault. Pump may not run and transmission pressure/cooling may be affected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours

Similar codes

P2797 P2799 P0620 P0562 P0616
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