As some here know I provide an instrument cluster repair service. In this post I just want to provide a piece of information that some may find useful.

The standard form of a CAN bus (a popular mechanism for communication between computer modules in vehicles) is commonly known - It consists of a pair of wires with the two ends connected together with 120 Ohm "terminating resistors". Modules connect to the bus via splicing to the pair of bus wires. The pair of terminating resistors are located within modules towards each end of the bus (typically the instrument cluster and ECU or GEM/BCM depending on the bus). The two bus wires being connected together via a pair of parallel 120 Ohm resistors means that there will be 60 Ohms of resistance between them.

Of note, typically in my experience a pair of 60 Ohm resistors is used 'in series' for a terminating resistor instead of a single 120 Ohm resistor, which of course amounts to the same thing.

When people are experiencing CAN bus communication issues they are often advised to use a multimeter to take a resistance measurement between the two wires (easily done via the OBD2 port). If the measurement is approximately 60 Ohms then this is said to prove that the bus is in good condition. If the measurement is approximately 120 Ohms then this proves than only one of the terminating resistors is connected. If the measurement is 'OL' then of course both terminating resistors would be disconnected. Any other measurement would be completely unexpected and indicate that something is very wrong.

The point of this post is to highlight the existence of an anomaly that throws a spanner in the works of this common diagnostics test, with some models of instrument cluster at least.

I was recently sent an instrument cluster from a 2007 Transit Connect. This model, like all of those that I've worked on, connects to two CAN buses and thus houses two (separate) terminating resistors. The designers of the circuit board of this model made provision for the boards to be constructed with either a pair of 60 Ohm resistors in series, or a single 120 Ohm resistor, for each CAN bus terminating resistor. A mistake seems to have been made however during construction. For one of the CAN buses a pair of 60 Ohm resistors was used, with the position for the alternative 120 Ohm resistor left empty. But for the other they have mistakenly fitted both the pair of 60 Ohm resistors and the single 120 Ohm resistor. This means that this CAN bus, when fully intact, will effectively have three parallel 120 Ohm resistors instead of two. Thus a healthy measurement of that CAN bus will be 40 Ohms instead of 60 Ohms, and if only the instrument cluster's terminating resistor is connected to the CAN bus wires (the one at the other end being disconnected for some reason) then you'd get a measurement of 60 Ohms instead of 120 Ohms, which could be mistaken for being a fully intact CAN bus.

This is the only model in which I recall having noticed this setup and can't see any others from a quick check of my collection of pictures. Since it may only prove relevant to Transit clusters I've thus posted this in the Transit subforum.

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On a separate note, I've only ever received two instrument clusters from Mk6 Transits. They looked almost identical, but proved to be very different. One had a pair of LCDs and a single 32-pin connector on the back. This suffers from the common problem of cracked connector solder joints. The other (the one mentioned above) had a single LCD and a pair of 26-pin connectors on the back and does not.

So the unknown answer is,

...... is this just a one off mistake, or are are all 2007 Transit Connects like this ?

Thanks for the information, something to file away in the little grey cells for later. 👍