Code
P1633
LEXUS
P — Powertrain
ECM Malfunction ETCS Circuit
Views:
UK: 41
EN: 58
RU: 46
AI status
Completed
Completed
100%
Causes
- Open, shorted or damaged wiring/connectors in ETCS circuit (throttle body, accelerator pedal, ECM)
- Poor or corroded ground(s) or 5V reference feed to pedal/throttle sensors
- Faulty electronic throttle body (throttle actuator motor or position sensors)
- Faulty accelerator pedal position (APP) sensor(s)
- Blown ETCS-related fuse or failed relay
- Intermittent battery/charging voltage (low voltage conditions)
Symptoms
- MIL (Check Engine Light) illuminated
- Reduced engine power / limp-in mode
- Poor or delayed throttle response
- Inconsistent or high/low idle
- Engine may stall at idle or during deceleration
- DTC P1633 stored and possibly other ETCS-related codes
What to check
- Read all stored/ pending codes and freeze frame data with a capable scan tool
- Check battery voltage and charging system (low voltage can cause faults)
- Inspect ETCS fuses and relays for continuity and proper operation
- Visually inspect connectors and wiring between ECM, throttle body and accelerator pedal for damage, corrosion, or loose pins
- Backprobe and verify sensor reference voltages (5 V), sensor grounds and signal outputs
- Use scan tool to monitor pedal position and throttle position sensor readings while operating the pedal
Signal parameters
- 5 V reference to APP and throttle position sensors (present and stable, ~5.0 V)
- APP sensor outputs typically vary between ~0.5 V (closed) and ~4.5 V (wide open) on each channel — two-channel correlation should track
- Throttle position sensor outputs should change smoothly with commanded throttle position (~0.5–4.5 V range depending on design)
- Throttle actuator motor supply ~12 V when commanded (dependent on design) and proper ground switching
- Sensor ground continuity to ECM (near 0 ohms when engine off)
- CAN bus/communication lines (if used) nominal voltages and no bus errors (if applicable)
Diagnostic algorithm
- Retrieve all codes and freeze frame; note any other ETCS/APP/throttle codes. Do not replace parts based on P1633 alone.
- Verify battery voltage ≥ 12.4 V with ignition on and charging system healthy. Low voltage can cause false ETCS faults.
- Inspect fuses/relays related to ETCS and replace if blown or faulty.
- Visually inspect connectors at ECM, throttle body and accelerator pedal module for corrosion, bent pins or water intrusion. Repair as needed.
- With a multimeter, verify the 5 V reference and sensor ground(s) at the APP and throttle body connectors with ignition ON. Replace or repair wiring if missing.
- Probe APP sensor outputs while slowly pressing the accelerator; confirm both channels move smoothly and correlate. Look for dropouts, noise or stuck values.
- Monitor throttle position sensor values with scan tool and command throttle actuator (if safe) to observe response. Check for erratic behavior or no movement.
- Perform resistance/continuity checks between ECM and throttle body/pedal connectors to detect opens/shorts; wiggle harness to find intermittent faults.
- If wiring and sensors test good, perform ETCS relearn/idle adaptation per manufacturer procedure and clear codes; retest for recurrence.
- If fault persists after verifying wiring and components, consider replacing throttle body or accelerator pedal module (based on test results) and retest.
- If all external components and wiring are good and replacement parts did not clear the issue, suspect ECM fault — confirm with manufacturer diagnostics before ECM replacement.
Likely causes
- Damaged harness or pin corrosion at throttle body or ECM connector
- Failing throttle actuator (motor) or throttle position sensors inside throttle body
- Failed or out-of-spec accelerator pedal position sensor
- Lost 5V reference or sensor ground from ECM
- Intermittent short to voltage or ground when harness is moved
- Faulty ECM when all other circuits test good
Fault status
Status
ECM detected malfunction in ETCS circuit. Possible causes: open/shorted wiring, failed throttle actuator or APP sensor, lost 5V reference or ground, blown ETCS fuse/relay, or ECM internal fault. May trigger limp mode and reduced throttle control.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
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LEXUS
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LEXUS: 2023
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ES 250
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