P0491

Code

LAND ROVER P — Powertrain

Insufficient flow in the secondary air injection system Bank 1

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 24 EN: 41 RU: 69

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Page language: EN

Causes

Failed or weak secondary air pump (mechanical or electrical failure)
Blocked or collapsed air hoses, pipes or intake/exhaust passages
Faulty secondary air injection check valve (stuck open or closed) or diverter valve
Faulty air injection solenoid/valve (electrical or mechanical)
Blown fuse, bad relay, poor power or ground to the pump or solenoid
Wiring harness damage or connector corrosion/intermittent

Symptoms

Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
Poor cold-start emissions, failed emissions test
Engine may run rough or higher emissions on cold start
Audible whine/growl from secondary air pump (if running) or no pump noise if failed
Possible exhaust odor or unusual noises from air pump area

What to check

Read freeze-frame and live data with a scan tool; confirm P0491 and any related codes (SAI or electrical)
Visual inspection of SAI pump, hoses, check valve, solenoid, and vacuum lines for damage, disconnection or blockage
Check fuses and relays for the SAI pump/solenoids
Listen for pump operation during key-on/start (compare audible behavior to expected)
Backprobe pump/solenoid power and ground with scan tool commanded ON; confirm ~12V supply and proper ground
Measure pump current draw to detect high or low load (indicates seized pump or poor flow)

Signal parameters

SAI pump commanded ON by PCM: switch to 12 V supply when active
Pump current draw: should be within manufacturer specified range (abnormally low = electrical/open; abnormally high = seized/blocked)
Air injection solenoid/valve activation signal: PCM duty cycle/ON command and confirmed solenoid ground/power
Oxygen sensor switching behavior during cold start (downstream O2 response expected when SAI operating)
Manifold/exhaust pressure or flow sensor readings where equipped (flow increase when pump ON)

Diagnostic algorithm

Verify code and any related DTCs with a scanner. Record freeze-frame data and attempt to recreate the condition.
Perform a thorough visual inspection: SAI pump, hoses, check valve, solenoids, connectors, and routing for kinks, restrictions or disconnection.
Check fuses and relays for SAI circuit; inspect connectors for corrosion or loose pins.
With key on/engine off, command SAI pump and/or solenoid ON using a scan tool and listen/observe for operation. Backprobe supply and ground for ~12 V when commanded.
If pump does not run when commanded, apply fused direct 12 V to the pump briefly to confirm mechanical operation. If pump runs only with direct power, trace wiring/relay/fuse/PCM driver.
If pump runs but code remains, inspect check valve/diverter valve for proper operation (some valves must close/open to direct flow). Remove and bench-test if necessary.
Perform a smoke/pressure test of the SAI plumbing to find leaks, collapsed hoses or blockages. Inspect the intake and exhaust ports where air is injected.
Check for exhaust backpressure or a clogged catalytic converter if flow is restricted despite pump and plumbing functioning.
Repair or replace failed components (pump, valves, hoses, electrical parts) and clear codes. Re-run readiness/test cycle and perform a cold-start test to confirm flow and that the code does not return.
If all hardware checks good and wiring/power grounded, consider PCM software update or replacement only after verifying all upstream items.

Likely causes

Failed secondary air pump (most common)
Collapsed/blocked hose or disconnected plumbing between pump and exhaust
Faulty check valve or diverter valve preventing proper flow
Electrical supply problem (fuse, relay, wiring) to the pump or solenoid
Exhaust restriction (catalyst) causing low measured flow

Fault status

⚠️ Status

P0491 — Secondary Air Injection System Insufficient Flow Bank 1. PCM detected lower than expected air injection flow during controlled test (cold start).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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P0491 — Insufficient flow in the secondary air injection system Bank 1