Code
P1657
LAND ROVER
P — Powertrain
Throttle motor relay driver turned off Malfunction of throttle motor relay Power circuit of the injection pump control module
Views:
UK: 16
EN: 29
RU: 23
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty relay in the throttle/injection pump power feed
- Open, short, or high-resistance wiring between battery, relay, and injection pump control module
- Corroded or loose connector or ground at relay, throttle motor, or pump module
- Faulty throttle motor relay (stuck open or coil failed)
- Control module driver (ECU/Injection pump control module) has disabled the relay due to an internal fault
- Intermittent battery/ignition supply or low battery voltage
Symptoms
- MIL (check engine) lamp illuminated
- Loss of throttle control response or limp-home mode (engine torque reduced)
- No power to the injection pump control module or related components
- Intermittent starting or running faults related to fuel delivery
- Stored additional related DTCs (power/communication faults)
What to check
- Read and record all stored DTCs and freeze-frame data; note ignition state and conditions
- Check battery state of charge and cranking voltage (should be ~12.4–14.5 V with engine running)
- Visually inspect fuses and relays related to throttle, pump control and ECU power; replace suspect items
- Inspect wiring harness, terminals and grounds for corrosion, damage or looseness at relay, throttle motor and pump control module
- Backprobe relay coil and control pins to confirm presence of ignition-switched 12 V and control signal from module
- Measure relay coil resistance and swap relay with known-good identical relay to rule out relay failure
Signal parameters
- Battery/ignition feed to relay: approx. 11–14.5 V with ignition ON
- Relay coil resistance (typical): roughly 50–200 Ω (check factory spec for exact value)
- Control module driver output (when commanding relay ON): should pull coil to ground or drive to specified logic level — measured voltage typically
- Control module output (when OFF): open/high-impedance; relay coil should see full feed voltage on one side and no ground on the driver side
- No excessive voltage drop across relay supply or ground (>0.5 V indicates high resistance)
Diagnostic algorithm
- Retrieve all codes and freeze-frame; note occurrence conditions and any related DTCs.
- Verify battery voltage and health. Recharge or replace battery if low; retest.
- Inspect and verify fuses and relay(s) for throttle/injection pump power. Replace any blown fuses and test swapping relay with known-good identical relay.
- Visually inspect connectors and harness for damage, corrosion, or water ingress at the relay, throttle motor, and injection pump control module. Repair as required.
- With ignition ON, backprobe the relay: verify constant battery feed at the relay supply pin and check the control pin for the expected module-driven signal when the relay should energize. Compare to signal_params.
- Measure relay coil resistance; if out of specification, replace relay. If relay coil is correct but no driver action, test whether the control module is commanding the relay (use a scan tool to command ON/OFF while monitoring the control pin).
- If the control module is not commanding the relay but should be, inspect wiring between the module and relay for open/short to battery or ground. Repair wiring faults and retest.
- If the module is commanding correctly but the relay still does not energize, check for voltage drop in the supply or ground circuits (high resistance). Repair wiring/grounds as needed.
- If wiring and relay check OK and the module output is abnormal (shorted, no output, or protective shutdown), consider module repair or replacement only after confirming wiring and power integrity and checking for software updates/TSBs.
- Clear codes and perform functional test/road test to confirm repair. Re-scan for return of DTC and address any secondary codes.
Likely causes
- Failed or dirty relay or fuse protecting the throttle motor / pump control feed
- Loose or corroded connector or ground at the relay or pump control module
- Wiring short to ground or open between relay and injection pump control module
- Control module output driver fault or protective shutdown
Fault status
Status
Throttle motor relay driver turned off — power circuit fault detected affecting the injection pump control module/relay. Relay driver disabled or relay power missing.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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