ABS unit swap: the Lotus 4-channel unit, part numbers and fitting

Why owners do it

The standard VX220 and Speedster ABS has two channels. Owners complained of it cutting in early on a bump or when swapping quickly from throttle to brake, then giving a hard pedal and very little braking for a moment ("ice mode"). Other owners said the standard ABS never bothered them, and one said it probably saved him from hitting a car at a roundabout. The alternative to a swap is a cut-off switch (see ABS cut-off switch: fitting), and for the pedal symptoms see brake pedal problems.

What you are swapping

• Only the electronic module on top of the hydraulic unit is changed. The hydraulic part with the brake pipes stays on the car, and the wheel sensors and loom are the same. One owner called it swapping the "brains".
• Owners say the 4-channel module comes from the Elise 111R and the Exige (some say other Lotus models too). The 111R is the one owners name as a 4-channel unit.
• Two owners (2011 and 2016) said the VXR220 has a 4-channel unit as standard, one of them saying his had 195-section front tyres. Another said a late Turbo unit was better for him. None gave a part number.
• The Elise and Exige built from 2011 use a different (Bosch) ABS with different hubs, sensors and a CAN connection. Owners say its parts are not compatible with the VX system, so those units are not a way in.

Part numbers and how to avoid the wrong unit

• The unit to look for: Lotus A120J6004S. The label on the unit says S108196012 (TRW 13091813), the TRW number, not the Lotus one.
• The standard 2-channel units: one owner (2020) summed up the numbers as 6002 for the Opel Vectra 2-channel, 6009 for the VX220 and Speedster 2-channel, and 6012 for the Lotus 4-channel. Another owner had also read that 6012 is the only 4-channel one.
• Check the number, not the sticker. Owners found 2-channel units with a Lotus sticker on them (S108196009, 13091809, 13216609), and an owner who owned one for years assuming it was a 4-channel. One owner said the 2-channel and 4-channel modules are the same hardware with different software, so you can't tell them apart by looking, only by the number or by testing. A swapped module in a crashed car is also easy to pass off.
• A Lotus Europa unit: one owner said the Europa unit is S108196009, one of the 2-channel numbers, and another said it is 4-channel. Another passed on from a Lotus contact that the Europa and VX units are the same. Treat the Europa unit as a 2-channel unit unless the number says 6012.
• The complete unit numbers: the parts diagram shows A120J6000F for the complete ABS control module, A120J6004S for the ECU kit and A116M0091S for the hydraulic kit. A seller's complete unit showed A116J6000F on the sticker, which one owner thought could be a VX220 unit with a different top.

Fitting

1. Slide the clip sideways and remove the connector from the module.
2. Undo the four Torx screws and lift the module off the hydraulic unit.
3. Fit the new module with new rubber seals, reversing the above.

Owners called it simple and a couple of minutes. (From a 2012 thread. One owner who fitted one said the access is easy on the VX but awkward on an Elise.)

New or used?

• A used unit that has already been activated can be plugged in and used straight away, according to several owners.
• A new unit needs activating (some say unlocking or resetting) with the right lead and diagnostic equipment before it works. Without that, owners said the ABS light stays on and the ABS doesn't work at all. It takes about five minutes on a car with a Lotus specialist's equipment.
• Several units can be activated on one car one after another. In the German group buys, 20 were done on one car and then posted out ready to use.
• In 2020 one owner reported that Lotus were taking months to supply new units, and another that the supplier was thinking of dropping them. Availability now is unknown.
• A drop-in unit from a tuning company was mentioned in 2018, said to need no Lotus activation and sold as track use only. One owner thought that label was for the German vehicle test, because a change like this isn't type-approved. That was his guess. We haven't seen anyone report fitting one.

The reset itself

• Owners (2017 thread) described it as plug in the Lotus lead, open the ABS page, press reset, unplug. It clears the ABS light that fitting a new unit triggers, and owners called it a reset and not programming. It took minutes for most.
• It needs Lotus equipment. Owners said a generic OBD reader won't do it and you need the Lotus lead and laptop. One owner suggested OP-COM could clear the fault, but others said it can't reach the ABS unit.
• Not every garage can. One owner (2017) had a specialist who couldn't get into the ABS page, and another whose tool failed to reset it on one visit, so a second place was needed. One owner said it took over an hour and some trouble before it worked. One was told by a garage it would be a long, difficult job, which other owners said was wrong. Ask beforehand whether they have the lead, and get one that has done it before.

Wheel sizes

• Owners in Germany said about 100 cars ran the Lotus unit, nearly all on 17-inch wheels front and rear, with different tyre ratios, and no problems. One said the unit adapts to different wheel diameters, and that the standard VX unit tolerates only about 2.5% difference.
• Another owner with a Europa on 16-inch front and 17-inch rear wheels said it worked great. A different Europa owner said that when he changed to 16-inch fronts on a unit set up for 17 inch, it did not adapt, and gave ABS fault lights and early ice mode. The two reports disagree, and neither is checked.
• Tyre sizes people reported (2016 and 2017): 205/50-16 front with 235/40-17 rear works perfectly for one owner. 195/50-16 front is fine for another, who had "huge issues" with ice mode on 205/45-16 R1R tyres on the same 7 inch wheels. Another owner asked about 215/45-17 front and 225/45-17 rear (about 1.6% circumference difference) and got no answer.
• One owner said the ABS compares wheel speeds, so it is the tyre circumference that matters and not the wheel size, and thought the Elise unit tolerates around 7%. That was from memory and not a figure from the maker. Another said most people stay on the standard Lotus sizes. An owner with a traction control box also said he would have to recalibrate it if the front/rear difference changes.
• An owner with 16-inch fronts and 17-inch rears on the Exige unit said it works great. One said the Exige unit was designed for a 16-inch front, and that some say it is better on 17s and some say worse.
• One owner on a supercharged Speedster ran the Lotus unit for years with 16 inch fronts and 17 inch rears, was happy, but measured only about 9.5 m/s² of deceleration where magazine tests of Elises and Exiges with the same brake setup reach about 12. He wondered whether the bigger front wheels trigger the ABS earlier than ideal. Nobody could answer that.

What owners reported

• Several owners said it transformed the braking, with no ice mode or hard pedal on road or track. One said it cuts in much later, regulates faster and lets you lock a front wheel briefly on track. One said it was like a different car on a bumpy road.
• An owner whose standard ABS cut in at random above 40 mph, and who had used a cut-off switch, found the front left wheel locked under heavy braking with it off. The Lotus unit solved both.
• One track owner thought the 4-channel is no help on track and still gets a hard pedal, so he switches it off. Another disagreed, saying it was the best mod he had made, even in the wet. Another thought the Lotus unit might simply have a higher trigger threshold, and not work better because it has four channels. That is a guess.
• One owner measured the standard ABS in the wet from 30 mph, 20.45 m with it on and 18.25 m with it off, and preferred it off. That was one test.
• An owner who fitted one together with fresh racing brake fluid and braided hoses reported excellent braking at a track day, and put most of the gain down to the ABS unit and less to the hoses.

Bleeding the brakes afterwards

An owner said the Lotus module is not recognised by the Vauxhall diagnostic tool, so the official bleed routine, which uses the tool to run the ABS pump, can't be done with it fitted. His approach was to swap the original module back for the bleed, and then refit the Lotus one. Another said most people, including garages, use the invert-the-front-caliper method instead, and the first owner replied that this doesn't clear air from the ABS unit. The Lotus module also needs Lotus diagnostic software. Compare brake fluid replacement.

Other ideas, not recommended

• A Daewoo Matiz module (S108196010): one owner said it works without reprogramming and is better than the original. Another owner compared the wiring diagrams and found completely different pin assignments for the wheel sensors, and on that basis put his original back and wouldn't test it. Another owner pointed out the Matiz layout splits the brakes diagonally, where the VX splits front and rear, which could release the wrong wheel. Nobody posted a result that settles it. Someone said maybe it isn't working, so it only seems better.
• The later Bosch system: one owner explained that using the later Elise system means using all its hubs and sensors and its own ABS unit, and may need a speed-pulse converter for the VX dash and engine management. Nobody did it.