P0946

Code

Generic P — Powertrain

Hydraulic Pump Relay/Control Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 38 EN: 83 RU: 38

AI status

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Page language: EN

Causes

Blown fuse for hydraulic pump circuit
Faulty hydraulic pump relay
Open, short or high resistance in relay control wiring or ground
Corroded/loose connector at relay, pump, or control module
Failing hydraulic pump motor (excessive current draw or low output)
Faulty PCM or relay driver circuit

Symptoms

Transmission or hydraulic system warning lamp illuminated
Loss of hydraulic pressure or degraded hydraulic system performance (reduced shifting, slow/soft actuators)
Vehicle enters limp/limited mode
Unusual pump or electrical noise from relay/pump area
Intermittent or permanent loss of a hydraulic-assisted function (e.g., transmission, steering assist)

What to check

Read and record freeze frame data and all related stored codes with a capable scan tool
Inspect fuses and fusible links for the hydraulic pump circuit
Visually inspect relay, pump, wiring harnesses and connectors for corrosion, damage, or loose terminals
Check for water intrusion or crushed wiring near the pump and relay
Using scan tool, command the hydraulic pump ON/OFF and observe status and parameters
Compare live data for commanded vs actual pump status and any related pressure or current parameters

Signal parameters

Control voltage at relay control pin: expected 0 V when OFF and approximately battery voltage (~12–14 V) when ON (or PWM signal if used)
Relay coil feed voltage: battery voltage with ignition on (check for voltage drop under load)
Ground continuity to chassis ground: near 0 ohms
Pump current draw: should be within manufacturer specification; common small electric pumps draw from ~1 A to tens of amps depending on design—compare to spec
If PWM controlled, check frequency and duty cycle per manufacturer data

Diagnostic algorithm

Connect a scan tool and confirm P0946 plus any related codes; record freeze frame and live data
Visually inspect relay, pump, connectors and associated wiring for damage, corrosion or water intrusion; repair obvious problems
Check/replace fuse and verify ignition feed voltage to pump relay power pin
With ignition ON, backprobe relay control pin while commanding pump ON from the scan tool. Verify control voltage or PWM is present and that it changes with the command
Measure voltage at the pump motor connector while commanding pump ON. If voltage present but pump does not run, suspect pump motor or internal failure
Measure current draw of the pump while operating (use clamp meter). Compare to specification; high current suggests internal pump fault or hydraulic binding, very low/no current suggests open/relay/coils problem
Check continuity and resistance of control circuit and ground to the PCM and relay; repair any high-resistance circuits
Swap relay with an identical known-good relay (if available) and retest
If wiring and relay check good but control signal from PCM is absent or abnormal, inspect PCM connector and consider module-level diagnostics or software updates before replacement
After repairs, clear codes and perform a road test or functional test to verify code does not return

Likely causes

Faulty pump relay
Poor ground or corroded connector at pump
Damaged wiring between PCM and relay coil/control pin
Pump motor drawing abnormal current (mechanical or electrical failure)
Fuse or fusible link open

Fault status

⚠️ Status

Stored when the PCM detects the hydraulic pump relay/control circuit output is outside expected range or performance versus the commanded request (open, short, high resistance, incorrect PWM, or abnormal pump load).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours