B12A6

Code

LAND ROVER B — Body

Auxiliary heater water pump

Brand: LAND ROVER

Type: B — Body

Views: UK: 14 EN: 48 RU: 15

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Page language: EN

Causes

Blown fuse or faulty relay for auxiliary heater pump
Poor or corroded electrical connector(s) at the pump
Open, shorted or high-resistance wiring in the pump supply/ground or control circuit
Faulty auxiliary heater water pump (mechanical seizure, worn motor, clogged impeller)
Control module output fault or software issue
Low battery voltage or poor chassis ground affecting pump operation

Symptoms

Instrument panel warning for auxiliary heater or secondary heating system
No secondary/auxiliary heater operation or reduced heater performance
Cooling system auxiliary pump not audible or not running when commanded
Engine bay fuse(s) for heater pump blown repeatedly
Erratic operation of heater (on/off or intermittent)

What to check

Read and record all active and historic DTCs and freeze frame data with a diagnostic scan tool
Visually inspect pump, wiring harness, connectors and ground points for damage, corrosion or coolant contamination
Check related fuses and relays for correct value and operation
With ignition on (or commanded ON via diagnostic tool) check for supply voltage at the pump connector
Backprobe control pin while commanding pump ON to check for PWM or switched 12 V output from control module
Measure pump motor current draw while running and compare to expected range

Signal parameters

Supply voltage to pump: nominal battery voltage ~11–14 V when running/commanded
Control signal: either switched 12 V or PWM duty cycle (0–100%) from control module — frequency varies by model
Typical running current (approx): 0.5–5 A depending on pump design; a stalled pump will show much higher current
Motor winding resistance (approx): low ohms range (typically ~0.5–5 Ω) — refer to manufacturer spec for exact value
No-voltage/open-circuit: infinite resistance; short to ground: near 0 Ω

Diagnostic algorithm

Confirm the code with a scan tool and record freeze-frame/fuel/temperature conditions. Clear code and attempt to re-create. 2) Perform a visual inspection of pump, harness, connector and mounting for damage, coolant contamination or corrosion. 3) Verify fuses and relays for the pump circuit; replace if faulty. 4) Backprobe pump connector with ignition ON and command pump ON via diagnostic tool: verify battery supply at the power pin and a ground or PWM control at the control pin. 5) If no supply, trace/repair power feed and check relay/ignition feed. If supply present but no control signal, test control module output; check wiring for open/short to ground/voltage. 6) With pump commanded ON, measure motor current. Very low/no current indicates open circuit or seized motor; excessive current indicates mechanical bind. 7) With battery disconnected, measure motor resistance; open or out-of-spec resistance indicates a bad motor. 8) Bench test the pump by applying correct voltage directly (observing safety and manufacturer instructions) to confirm mechanical operation and flow. 9) Inspect coolant lines and pump inlet for blockages or frozen conditions causing no flow. 10) If wiring and supply are good but pump fails tests, replace pump assembly. After repair, clear codes, perform a heater system function test and road/test cycle to confirm code does not return. 11) If wiring and pump test OK and control signal absent or stuck, suspect control module or software — consult manufacturer diagnostics and update software if applicable.

Likely causes

Faulty pump motor or seized impeller
Open/high-resistance wiring or corroded connector at pump
Blown fuse or failed relay
Control module output or driver failure

Fault status

⚠️ Status

Auxiliary heater water pump — electrical circuit or performance fault detected. The control module has logged reduced/no pump operation or an electrical anomaly in the pump circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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