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• The electronic-fault (zig-zag box) lamp on a 1998 Renault Clio II almost always means the Engine Control Unit (ECU) has logged a sensor, ignition- or wiring-related error.
• The lamp coming on only at a steady cruising speed (≈ 2 800-3 200 rpm) narrows the most probable causes to:
– Worn Throttle-/Accelerator-Position Sensor (TPS / APS) “flat-spot”
– Ignition coil pack beginning to break down when warm
– Intermittent wiring loom or earth fault (especially near LH suspension turret)
– Age-related crank- or coolant-temperature sensor drift
• You do NOT fix the problem by guessing parts: first read the Diagnostic-Trouble-Codes (DTCs) with an OBD-II/CLIP scanner, confirm the faulty circuit, then repair or replace only the proven culprit, clear the codes and road-test.
Why the lamp appears at constant speed
• During cruise the ECU is in “closed loop”, relying mainly on TPS/APS, MAP (or MAF on some 1.4/1.6), crank- and coolant-sensors plus the upstream λ-sensor to trim fuelling and ignition.
• A component that is intermittently open-circuit, noisy, or heat-sensitive will start outputting an implausible value after a few seconds in this steady state; the ECU flags this with the electronic-fault light.
Component-by-component probabilities and tests
A. Throttle/Accelerator Position Sensor (very common)
– Symptom: light comes on at exactly the same pedal position, sometimes accompanied by a momentary hesitation.
– Test: live-data graph on scanner; %-value should climb smoothly. A sudden drop or jitter = worn track.
– Bench check: 3-pin potentiometer, ~0.5 V idle – 4.5 V WOT, no dead spots.
– Fix: replace TPS; on cable-throttle engines recalibrate by key-on 10 s, key-off.
B. Ignition coil pack / COP (common on 1.2 8v/1.4 16v)
– Heat cracks or internal arcing produce misfire counts only at cruise load.
– Test: swap with known-good, or check secondary resistance 7–10 kΩ and look for carbon tracking.
C. Crankshaft Position Sensor (CPS)
– Early Clio II sensors had poor shielding: resistance drift >250 Ω or metal filings on tip cause sync loss.
– Renault supplied a revised, screened sensor + short harness; inexpensive pre-emptive fix.
D. Coolant Temperature Sensor (CTS)
– Green-bodied units absorb coolant and read –10 °C or +130 °C briefly → ECU enriches mixture, sets fault.
– Live data outside 70–105 °C when engine fully warm = replace.
E. Wiring loom chafing / earth straps
– Loom behind LH strut tower protected by a steel “U” guard; edge rubs through insulation.
– Poor engine-to-chassis earth raises sensor ground, confusing ECU.
– Inspect, splice, sleeve, add 16 mm² braided earth strap to gearbox bolt.
F. Upstream λ-sensor, MAP sensor, brake-/clutch-switch, pedal switch, ECU itself (less frequent but possible).
Typical DTC mapping (Renault ISO 9141-2)
• P0120-P0123 → TPS/APS circuit
• P0300-P0304 → random / specific misfire (coil, leads, plugs)
• P0335 → crank sensor A circuit
• P0115-P0118 → coolant temperature sensor
• P0105-P0108 → MAP sensor
• P0130-P0135 → front oxygen sensor
Why guessing parts costs more
• Coil, TPS, sensors are each £25-£70. One wrong guess equals the price of an ELM327 or a one-hour diagnostic session that tells you exactly which circuit is faulty.
• Community and dealer bulletins (2023-2024) still rate TPS and coil packs as the top two Clio II electrical-fault triggers.
• Revised crank sensors with integrated shielding are stocked by Renault and aftermarket suppliers; high success rate in intermittent “electrical fault + stall” cases.
• ECU re-flashes for early D7F/D4F engines are obsolete; modern solution is usually sensor/loom repair, not reprogramming.
• Owners increasingly add extra ground straps and dielectric-grease all multi-way connectors to prevent recurrences.
OBD-II live-data snapshot at the moment the lamp lights (example values):
RPM 2920 rpm (stable)
TPS 23% → 0% spikes (wrong) ← suspect TPS
MAP 38 kPa (reasonable)
Coolant 88 °C (OK)
Misfire Ct Cylinder 2: 4 counts/s ← confirm coil if presentA single aberrant signal (TPS plunging) amidst otherwise steady data immediately isolates the fault.
Analogy: think of the ECU as an orchestra conductor; if one violin (sensor) squeals out of tune only on a sustained note, the conductor stops the performance—your warning lamp.
• Driving with a lit electronic-fault lamp may place the vehicle outside European Emission Standard compliance and can overheat the catalytic converter.
• Clearing codes without fixing root cause is illegal in many jurisdictions if the vehicle is sold.
• Dispose of replaced sensors/coil packs via authorised electronic-waste channels.
• Without the exact DTC list any answer remains probabilistic; always start with code read-out.
• ECU failure is rare (<3 % of cases); replace only after sensor and loom are proven good.
• Some late-1998 Clios still use pre-OBD protocols—use a CAN-capable scanner with ISO 9141 / K-line support.
• Review Renault Technical Note NT 3022A (Clio II intermittent electrical fault) if you have dealer access.
• Investigate retrofit of the later “true-fly-by-wire” accelerator pedal assembly, which eradicates APS wear issues.
• Explore open-source “RenoDiag” logging software for long-term trending of sensor noise.
The electronic-fault lamp illuminating at a constant cruising speed in a 1998 Clio II almost always traces to a single sensor or wiring defect under steady-state load—most often a worn TPS/APS or a coil pack that fails when warm.
Read the DTCs, watch live-data to pinpoint the errant signal, repair or replace that component, verify clean wiring grounds, clear the fault memory, and the problem is solved permanently and cheaply.