Vehicle Speed Sensors – R J Engineered Solutions

Vehicle speed sensors for every rear engined VW to Subaru or inline VW engine conversion application

……. (as long as you’re using the original VW speedometer), including the difficult ones such as the 1982 / 83 T25 / T3 / Vanagon:

Price: from £44.17 GBP + VAT (£53)

Rear engined air cooled VW models – M18 VSS:

Price: £56.25 GBP + VAT (£67.50)

All air cooled VW models have screw on speedometer cables, and the vehicle speed sensor screws between the speedo and its speedo, so no modification to any VW parts needed. Our sensor is shorter than similar models available elsewhere. Shown here fitted to a bay window bus instrument cluster:

Part no. 800-00064, for Subaru engine conversions
Part no. 800-00065, for VW inline (GTi or TDi, etc) engine conversions. Sometimes also used in early Golf, etc conversions to other VAG engines

Supplied with either 2m of unterminated cable if you’re not using our harness work, or with the relevant connector to plug in to your front extension harness already fitted if you are.

If wiring the sensor in to your engine management (or GPS, cruise control, etc) yourself, the positive supply should be fused to suit the wiring used (typically a 10A or 15A fuse, although the senor only draws a few milliamps).

Note: these models are not protected against reverse polarity, so double check your connections before turning the power on if wiring one up yourself.

T25 / T3 / Vanagon VSS. all 1984 onwards and some 1982 / 1983

Price: £41.67 GBP + VAT (£50.00)

Part no. 800-00018, for Subaru engine conversions
Part no. 800-00066, for VW inline (GTi or TDi, etc) engine conversions. Sometimes also used in Golf, early T4, etc conversions to other VAG engines

Supplied with the connector fitted as shown, and either with the opposite connector and terminals loose, for you to install if you’re not using our harness work), or with them installed on your front extension harness if you are.

These models are protected against reverse polarity and output overload, making them hard to kill by connecting incorrectly (even if you deliberately try!). If wiring the sensor in to your engine management (or GPS, cruise control, etc) yourself, the positive supply should be fused to suit the wiring used (typically a 10A or 15A fuse, although the senor only draws a few milliamps).

See below for more information on how to identify the different T25 / T3 / Vanagon speedometer types

T25 / T3 / Vanagon VSS. required for some 1982 / 1983 models:

Price: £56.67 GBP + VAT (£68.00)

Part no. 800-00045, for Subaru engine conversions
Part no. 800-00067, for VW inline (GTi or TDi, etc) engine conversions

See below for more information on how to identify the different T25 / T3 / Vanagon speedometer types

Rear engined water cooled VW models – you need to check which VSS type you need if 1982 or 1983:

The water cooled models use clip on speedo cables, so the screw on speed sensors from air cooled models can’t be used. There are 3 different types. They all have built in speed sensor locations intended for VW’s analogue cruise control sensor, next to where the cable clips on, but do not all use the same sensors:

The sensor recess is covered by a plastic cover moulded into the speedo housing as shown above. This cover is designed to be easily broken away to fit a sensor, and has a tab so it can be gripped with pliers. It’s marked ‘abgrif’ or ‘impuls geber’ depending on the speedo type.

Which sensor type you need for 1984 models onwards is easy – the speedometers all identical in terms of how the sensors fit (shown as Water cooled VW T25 / T3 / Vanagon speedometer Type C, above).
For 1982 / 1982 models it is not so straight forward, as there are two designs. Water cooled VW T25 / T3 / Vanagon speedometer Type A, as shown above can only work with a speed sensor with 2 prongs. Water cooled VW T25 / T3 / Vanagon speedometer Type B, as shown above, can work with either the ‘2 prong’ sensor type or the sensor used by all the 1984 –> models – we recommend the latter, as they’re cheaper. The problem is that until you break away the sensor recess cover on the 1982 / 83 models and look inside, you will not know which type you have, as they are externally identical.

All of our speed sensors for the water cooled applications have built in protection against output overload, reverse polarity and over voltage, making them very difficult to damage by incorrect connection even if you deliberately try.

Speed Sensor Wiring – All Types. ‘Plug and play’ if using our engine management harnesses. Supplied with instructions showing which sensor terminals are which if you are wiring them up yourself.

If the objective is for your engine conversion to run without annoying symptoms and error codes, Subaru engine management requires a vehicle speed input. Many other engines used in conversions also require a speed signal. We also make speed sensors for some of them too – in particular the VW TDi and petrol inline 4 engines (GTi. 1.8, etc), which require a different spec signal to Subaru. In a pre-CAN bus Subaru the signal is created either by the Subaru instrument cluster (–> ~ MY98), or a sensor screwed into the gearbox. The easiest, most reliable source in a VW is to use a sensor which creates the necessary signal from the rotation of either the speedometer cable or speedometer, depending on the VW model. Air cooled VW models did not have any provision designed in for creating a vehicle speed signal, but water cooled models did – it was used for cruise control. These used an analogue speed signal from an inductive sensor which is not compatible with Subaru or the VW inline engine management. They require a digital signal.

We make vehicle speed sensors for every rear engined VW application, including the difficult ones such as the 1982/83 T25 / T3 / Vanagon (cast zinc rather then plastic speedo mechanism with clip on speedo cable). We can even make them for obscure applications such as a water cooled T25/T3/Vanagon model which still need to use the original analogue speed sensor for VW cruise control, but also need a digital signal for the engine management. For some unusual applications we can make special sensors with two independent, different spec outputs. All types just screw into VW parts which you already have (unless you no longer have the original VW dash instruments).

Vehicle Speed Sensor FAQ:

20mA maximum. All types for water cooled rear engined VW models (i.e. with a clip on speedo cable) have over current protection built in, so if you exceed this, they just stop working until the cause of the over current is rectified. All types for air cooled VW models (i.e. with a screw on M18 x 1.5 speedo cable) do not have output overload protection. This is not an issue with any normal application, but if you’re using one for something unusual, measure the current to check it doesn’t exceed 20mA before connecting the sensor. Make sure you measure the total current if you are using the speed signal for more then one system – the usual cause of higher a current. normal multiple system use would be engine management and cruise control, and would typically still be below 20mA.

OEM speed sensors for all the common applications (Subaru and VW inline petrol and TDi) do not give out a voltage. They are open collector sensors, used in circuits where the signal voltage that you can measure comes from the circuit they’re connected to (via a pull up resistor), not from the sensor. There is a lot of confusion about this, including bu some who make their own speed sensors (presumably they didn’t design them – whoever did will understand this), as proven by the amount of times we’ve been asked this question. All of it comes from those who do not understand vehicle speed sensors or the circuits that they connect to, and their willingness to share misinformation online. If someone tell you that your Subaru or VW engine management application needs a sensor which gives out a signal with a certain voltage, the are proving their lack of understanding by doing so. Our speed sensors are suitable as supplied for use with signals at all the usual voltages in engine management (typically 5-15V).

Yes, but to do so you need to know what you’re doing! In Subaru’s, the signal was shared by the engine management, speedometer, cruise control, automatic transmission ECU, etc. The things to look out for are:
1. That you don’t exceed a total of 20mA current sink.
2. That the systems that you are connecting to either all run at the same voltage, or that you add diodes to prevent the higher voltage circuit(s) back feeding the lower voltage ones. This typically won’t be the case with systems intended to work together sich as Subaru engine management and cruise control, but may well be if they systems were not originally intended to work together. A 1N4148 signal diode between the signal wire from each circuit and the sensor, with it’s cathode towards the speed sensor would work fine if they are different voltages.

If the speedometer is compatible with digital open collector sensors, yes. If it is an aftermarket speedometer, it will almost certainly be compatible with many different sensor specs (more so the more modern the speedometer), and will have easy user calibration built in. However, if it is an OEM speedometer from another vehicle, it will not have easy user calibration built in. Even if the sensor output is electrically compatible, you will need to use additional hardware to do the calibration. We used to stock a product for this, but as the demand was virtually zero, we don’t any more. Making a speed sensor with built in adjustable calibration has been on the ‘to do’ list for a long time (mainly because it would be an interesting project), but it never gets near the top of the list as they’re only needed for very niche applications. If you have some weird application where you need loads of them, get in touch, and maybe it’ll move up the list!

For an application where simple conventional vehicle speed sensors such as ours are readily available, using GPS to create a vehicle speed signal has to be an ultimate example of using a sledge hammer to crack a nut. A ridiculous solution to a simple problem. It is also not legal here in the UK if used to drive the speedometer (although the chances of ever getting into any trouble for it must be near zero). Also, the fact that to work at all, GPS speed sensors always have a microprocessor controlling them, and extra features can be added via it at virtually no cost, yet many don’t even have calibration built in is a joke. It could be added for the cost of a couple of switches and resistors (i.e. a few pence), plus some more lines of code. The only logic for this is that the manufacturer prioritises minimal cost over making a good product, or just doesn’t understand the potential applications.
That’s not to say GPS speed sensors don’t have sensible applications. They do, but they’re extremely niche. We’ve done the engine management wiring for a few Subaru powered hovercraft over the years, including an ocean going one. With no other means of accurately measuring vehicle speed, GPS speed sensing in a hovercraft is probably the way to go.
We were also asked to do the wiring work for a Subaru powered Ekranoplan back before GPS speed signal generation was viable, but turned the job down over the builder’s lack of interest in the detail of how he was going to provide it with a suitable speed signal. He didn’t seem to understand the very real risk of the engine just stopping because he wan’t providing it with a suitable signal. He was effectively asking us to be involved in a project in which he’d be flying at very high speed a few feet above water (or ground?), in which we knew the engine would likely stop. Err, no thanks. If GPS speed signal generation was available back then, we’d have taken the job on.

They vary with ECU part number, but will be one or two of the following, with the most common first:

After you’ve been driving at high rpm, and then suddenly stop, instead of dropping to idle, the rpm drops to zero. The engine stops completely ‘cleanly’ – exactly as if you had turned it off (i.e. the engine doesn’t struggle to keep running but eventually lose). This typically happens when you stop at the end of the slip road after pulling off a dual carriageway or motorway, but wit certain ECU’s it happens almost every time you stop regardless of what rpm you were doing previously.
The engine cutting out when you’re driving at high rpm and have not moved your foot on the throttle for about 10 minutes. Some customers report the engine re-starting (i.e. bump starting itself, as you’re still moving at speed) as son as you move your foot on the throttle, others report having to turn the engine off and on again before it runs normally again (until next time).
An artificially low rev limit. We did get to measure this as it happened using Subaru dealership diagnostic tools, and on the engine in question it’s rev limit was 3999 rpm instead of 6250 rpm, which seems typical. It’s a ‘hard cut’ rev limit (i.e. it just turns the ignition off on all cylinders at once), so is quite violent especially if you don’t lift your foot off the throttle.

We never intentionally experiment with any of these symptoms, as we would never run the engine without a speed sensor. As such almost all the data we’ve collected on them has come from customers, but we’ve seen all of them happen many times, and have kept details of which symptoms which ECU’s get when that has been available from the customers.

If your objective is to have the engine run as it did in the Subaru, with no error codes (it should be, with all but a few specific ECU models), then no. If you want to treat your conversion as an experiment, then that’s up to you! We’d recommend not doing so without a reasonably good understanding of what symptoms of running without a speed sensor you can expect though, so you know what you can expect. One of them in particular will worry you a lot, and could be dangerous if it happens and you don’t understand what’s happening. But none of them will leave you stranded at the side of the road broken down.

If you have run a Subaru powered VW for a long time without a speed sensor, especially if the engine is from a model later then about 1992, then the chances are that you’ll be familiar with some of the associated symptoms even if you don’t realise it. At least here in the UK, many conversions have been installed by so called ‘specialists’ who have next to zero understanding of the systems they work on. They routinely ripped out all of the diagnostics (presumably so their customers cant see all the error codes that they have) and all sorts of other features including the speed sensor wiring. There is no possible other explanation for apart from a total lack of understanding. They then fob off their customers with every excuse under the sun about all the problems their terrible installation creates. If this sounds familiar, you’re being lied to. Those responsible may not know they are lying though – they just don’t understand what they are doing, and have never learned to raise their game despite being involved in many years. They’re totally out of their depth (yet clearly are good salesmen). Look into whether they design and manufacture any electronic components for their engine conversions – they don’t, and wouldn’t have a clue how to.
Do your homework up front if looking for someone install your engine conversion, at least here in the UK. Almost all of the worst Subaru engine conversion bodges we have ever seen are not the work of amateurs, but the work of certain so called ‘specialists’. Their terrible reputation is very easy to find if people were only to look for it up front, rather than when it’s too late.

This will sound hard to believe, or unlikely, but it is real. We didn’t believe it until the 4th or 5th customer who had chosen to try running their conversion without a speed sensor had all reported the same thing when ordering one. Many others have reported it since too, and a pattern has emerged where this only affects a small number of particular ECU part numbers.
Some Subaru ECU’s can seem totally happy without a speed signal for fairly long periods of time or a few thousand miles, then suddenly object, typically then giving both error codes and symptoms.

Assuming your speedometer is working normally, then more then likely you need to change the state of the neutral position switch input by plugging the NPS wires together or unplugging them. With almost all ECU’s this solves the problem for good. However, there some ECU part numbers which are not happy with the NPS always being in either state. They need a working neutral position switch.
If your speedometer is not working (usually due to a broken cable, worn cable drive hole on the front LH wheel bearing cap, or missing circlip – common faults especially on 2wd T25 / T3 / Vanagon models), this is why you have vehicle speed sensor symptoms. With the speedo not working, the speed sensor cannot create a speed signal. You would think this would be obvious to whose who are already familiar with the vehicle speed sensor (typically because they fitted it themself), yet multiple times we have had folks not put two and two together and realise this.

Also, if your speedometer needle bounces an awful lot (always due to a kinked cable), this can cause problems. The speedo cable slows or stops as it reaches the tight spot each revolution, then winds up until there is enough torque to overcome it and spins way faster than the actual vehicle speed to catch up. This causes the needle bounce. However, Subaru engine management is also fast enough to read this much higher speed (they clearly doesn’t average the vehicle speed reading over a period of time, but read the signal in or almost in real time). It can be higher than the ECU understands, and this can cause problems. This is especially likely with JDM spec Subaru engines due to the Japanese manufacturers ‘gentleman’s agreement’ 180 kph (112 mph) maximum speed limiter on all JDM modes on many model years. We’ve also seen this speed limiter feature in certain non JDM Subaru models too. Most don’t have it, but some do. Probably models which were derived from spec’s originally sold in Japan (one of the ones we’ve seen definitely was), then tweaked to meet other markets emissions requirements without removing the limiter.
Symptoms of not having a vehicle speed sensor can persist when you do have one due to a not uncommon error in the engine management wiring work too.

If we did your the engine management wiring work for your VW conversion, connecting up the speed sensor is easy. Especially if you went for our ‘front extension harness’ option, the sensor connector is already there – you just fit the sensor to your speedo and plug it in. If you didn’t go for the front extension harness option (almost every customer does), the three wires for the speed sensor are clearly identified – you just have to extend them to the front and fit the provided connector to plug in to the sensor.
If someone else did the engine management wiring work for you, you’ll need to ask them where they terminated the speed sensor wires, how they’re identified, etc.
If you’ve done the engine management wiring work yourself, you’ll already have the information that you need to wire up the speed sensor.

The first speed sensors we ever made were CV joint mounted. We had consistent problems with them, and were never really happy with their vulnerability under the VW. We never sold that type (well maybe sold one) before switching to speedo / speedo cable mounted ones. They’re much less vulnerable there, and the location also suits models without CV joints. Apart from the first batch of our T24/T3/Vanagon speedo mounted sensors (which had a design error back in around 2008, and were subsequently all replaced at no cost to the customer), the speedo / speedo cable mounted sensors have proven to have OEM reliability.