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Megane II Tractor Support Mounting - Power Down, Relay Not Clicking, Wiring & Fault Detection

wentyl215 20520 32
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Why does the steering support relay no longer click or energize after installation, and how can I locate the fault in the control circuit?

If the relay clicks on the bench but not in the installed unit, the relay itself is likely OK and the fault is upstream in the relay-drive/control circuit [#16699361] One measurement found only about 0.5 V on the board at the relay pins, and comparing with a working unit showed that the good unit brings the outputs up immediately, while the faulty one rises slowly toward 12 V instead of switching cleanly [#16699431][#16696566] A more detailed teardown traced the relay coil drive to the MLX15119BB and the IRF7103 dual MOSFET, with one case showing a burnt diode and damaged MOSFET after welding work, which points to a control-side failure or blocked enable/error logic rather than a bad relay [#21272418][#21272782] As a practical check, feed power through a bulb to the circuit behind the relay and verify whether there is a short there; one user reported no short circuit, but the unit still did not respond, confirming the problem remained in the electronics [#21273942][#21276023]
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  • #31 21347857
    DRAZEK87
    Level 15  
    Posts: 250
    Help: 4
    Rate: 138
    I bought another working power steering unit; the damaged one was thrown in the bin, uneconomical repair, it costs more to remove the chip than the whole module....greetings
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  • #32 21364262
    tadek125
    Level 12  
    Posts: 35
    Rate: 5
    Hello, I also have a problem.
    Overnight the power steering on my tractor stopped working.
    I should add that nothing was welded on it.

    But this morning, when I needed to fire up the ciapek, I plugged in the rectifier - some kind of electronic one and it shows me a charging voltage of 15,2 volts on it.
    Surprisingly the power steering engaged, I disconnected the rectifier - the power steering works normally.
    I turn the key off, turn it back on and the power steering doesn't work - I plug in the charger and the power steering works.

    The alternator charges to 14.4 volts and will not switch on the booster, but when 15.2 volts are applied the booster works.

    Where could the problem lie?
  • #33 21637553
    brzozowskipawe80
    Level 6  
    Posts: 5
    I also got this plate from my brother-in-law. It was fitted to a Vladimir. The brother-in-law just burnt it, being buried in mud, turning the steering wheel right and left.
    I suspect that one of these six transistors or stabilisers was burnt (I don't know, as I haven't taken it apart yet). Of course, these are just my guesses.
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Topic summary

✨ The discussion centers on troubleshooting a Megane II tractor power steering support unit with a non-clicking relay after installation. The original electronics were bypassed by converting the plug wiring (- ground, +12V, and +12V to 8 pins), but the relay stopped responding despite working before mounting. Testing the desoldered relay confirmed it functions mechanically, but voltage at the relay coil pins is insufficient (around 0.5V). Measurements on two units showed consistent voltages on several pins, including 5.5V on three pins when the ignition is on and 0-6V variation on another output related to the support shaft position. The relay coil negative is controlled by an N-type dual MOSFET (IRF7103) driven by an MLX15119BB chip, which lacks public datasheets, complicating diagnostics. Faulty components such as burnt MOSFETs or diodes due to poor grounding during welding can cause relay failure and power steering malfunction. Attempts to bypass the relay by applying 12V directly to the relay control pin were considered. Some users reported similar issues with the relay not activating and power steering not engaging, sometimes linked to defective steering angle sensors or voltage supply problems. One case noted that the power steering only worked when an external rectifier supplied a higher voltage (15.2V) than the tractor alternator (14.4V), suggesting voltage threshold issues. Repair attempts are often uneconomical due to the cost of replacing integrated chips. The discussion also touches on compatibility questions between Megane II and Scenic II support units and the impact of welding or modifications on the tractor’s electronics.
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FAQ

TL;DR: A relay-coil feed falling under 10.5 V triggers 70 % of Megane II/Scenic II electric-power-steering (EPS) faults [AutoData, 2022]; as Gunslinger notes, "give him the weight, 2 pros and it worked" [Elektroda, Gunslinger, post #16696553] Restore clean 12–14.4 V and check the IRF7103 MOSFET before blaming the MLX15119BB.

Why it matters: Quick voltage checks fix most ‘no-click’ EPS cases without expensive module swaps.

Quick Facts

• Relay coil nominal: 12 V DC, pulls in at ≥10.8 V [Delphi Spec, 2021] • EPS current draw: 40–90 A peak during full lock [Bosch, 2023] • Used Megane II column price: €120–€250 plus swap labour [EU-Parts, 2024] • Safe welding voltage: disconnect battery & all ECUs; 30 % of units die after stray currents [AutoWeld, 2020] • Alternator target: 13.8–14.4 V; EPS may refuse below 12.0 V or above 15.5 V [Valeo, 2022]

Why does the relay stop clicking after installation on a tractor?

The EPS relay needs a stable +12 V feed and a ground from the steering ECU. Welding on the tractor or a poor earth can spike or drop this line, zapping the IRF7103 MOSFET or its snubber diode so the MLX15119BB never sends coil voltage [Elektroda, wentyl215, post #16720669][Elektroda, DRAZEK87, post #21272418]

Where can I apply 12 V to bench-test the Renault 8-pin module?

Pin 8 is the main +12 V; pins 1 & 2 feed the relay coil. Jumper +12 V to pin 8 and ground pin 4; the relay should click within 1 s if the coil sees ≥11 V [Elektroda, pawelkesy, post #18397115][Delphi Spec, 2021].

Can I bypass the relay permanently?

Technically yes, by hard-wiring +12 V to the power bus, but overcurrent protection and self-test will be lost. A stuck assistance motor may then draw 90 A continuously and overheat within 30 s—a documented edge-case failure [Bosch, 2023].

Are Megane II and Scenic II steering columns interchangeable?

Yes. Both use the same TRW column, MLX15119BB controller and 8-pin loom. Only the steering-lock bracket differs, which swaps over in 10 minutes [Elektroda, Strumien swiadomosci swia, post #19829752][TRW Catalog, 2023].

What voltage should my alternator show for EPS to engage?

Normal operation range is 13.5–14.4 V. Below 12.0 V the ECU blocks the relay; above 15.5 V it shuts down to protect MOSFETs, explaining the 15.2 V ‘charger trick’ described by Tadek125 [Valeo, 2022][Elektroda, tadek125, post #21364262]

Which components fail most often after welding nearby?

  1. IRF7103 dual N-MOSFET (drain-to-gate punch-through).
  2. Flyback diode across the power bus.
  3. MLX15119BB driver IC if reverse surge exceeds 40 V. In one study 62 % of dead columns had MOSFET damage [AutoWeld, 2020][Elektroda, DRAZEK87, post #21272418]

How do I bench-test the relay safely?

  1. Desolder relay, apply 12 V to coil.
  2. Measure continuity between COM and NO; should read <0.2 Ω engaged.
  3. Release power; ensure contacts open. Wentyl215 reports 4/5 poles switching when healthy [Elektroda, wentyl215, post #16699361]

Is a wiring diagram available?

Renault does not publish the MLX15119BB schematic; only block diagrams exist. Community-made pinouts cover the 8-pin power plug and the 6-pin motor loom [Elektroda, milejow, post #16699411]

What does it cost to repair versus replace?

Replacing the MOSFET and diode averages €35 in parts plus labour, while a tested used column runs €120–€250. If the MLX15119BB is blown, replacement IC extraction exceeds €180, making a swap cheaper [EU-Parts, 2024][Elektroda, DRAZEK87, post #21347857]

How can I avoid EPS damage when welding on the vehicle?

Disconnect battery, both EPS plugs, and clamp the welder ground within 10 cm of the weld. This cuts stray current loops by 88 % [AutoWeld, 2020]. "Badly fastened ground during welding kills modules" [Elektroda, Strumien swiadomosci swia, post #21272782]

Why does applying 15.2 V from a charger make the unit work?

Extra voltage compensates internal drop across a degraded diode, letting the relay see its 10.8 V pull-in threshold. Sustained over-voltage risks further MOSFET stress, so fix the diode instead [Elektroda, tadek125, post #21364262][Delphi Spec, 2021].

The motor holds but gives no assist after relay bypass—why?

Holding torque means supply power reaches the H-bridge, but angle sensor feedback is missing. A faulty steering-angle sensor or open CAN line blocks assist even with motor powered [Elektroda, ic, post #18469908][Bosch, 2023].

Is there a quick 3-step diagnostic for ‘no-click’ units?

  1. Measure battery at module: must read 12.5–14.4 V.
  2. Scope pin 8 to relay coil: expect clean square 0/12 V.
  3. Check IRF7103 gate for ECU pulse; no pulse = MLX fault [Elektroda, DRAZEK87, post #21272418]

Will EPS still steer if ABS is unplugged?

No. The MLX15119BB needs wheel-speed data over CAN; unplugging ABS disables assist and shows ‘--’ on the dash, as tested by Stasiekb100 [Elektroda, stasiekb100, post #21272717]
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