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Home » Engine Management » Mazda 6 est 2000 petrol 2006 fault codes u1900 u2516

(Fault and Ignition Issues - Fault Codes and Diagnostics)

Posts: 8
Hi this vehicle as come in with these fault codes it runs from cold then stops
with no spark at the plugs
any ideas please
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Thanks for posting your question - I have done some research based on the information provided and I will try to assist you in the resolution of this issue.

Unfortunately, it doesn't sound like the solution to this particular issue is likely to be straightforward - and will ultimately depend on diagnostic procedure (or someone who has seen this exact issue before).

Looking at the information have provided I have managed to find the following (from Mazda):

DTC U1900 - Reported by Instrument Cluster - Description: 'Communication error to other modules'
DTC U2516 - Reported by Instrument Cluster - Description: 'CAN system communication error'

Possible causes for both codes relate to CAN wiring harness issues (e.g. open or short circuit).

Based on these being the only codes reported, I would advise that you start by checking the connection to the instrument cluster and evaluating its integrity. If the connection is ok, I would then proceed to check the condition of the wiring harness from the instrument cluster to the nearest splice (as the Instrument Cluster is a terminating node on this particular network) - it may also be worth checking power and ground to the instrument cluster.

When the vehicle cuts out, you could try taking CAN line resistance measurements from the OBD connector - this should be done with the battery disconnected.

You should be conducting basic CAN diagnostics, you should see:

- Resistance of circa 60 ohms across CAN high and CAN low.
- No shorts to ground, power (on either side) or to each other.

If you have an oscilloscope, this could also be used to identify the issue (connect to CAN high and low, with a good ground reference - see what happens on the network when the vehicle cuts out, does either side go to ground/power?).

If you see 120 ohms when the vehicle is in its failed state, this means that the CAN circuit is open and you have lost a terminating node.

As mentioned previously, there does not appear to be an easy resolution to this fault, you will have to pick a place to start and conduct basic CAN diagnostics in order to rule out a CAN issue.

Due to the intermittent nature of this fault, I know that carrying out the above will not be straightforward.

I hope this helps.

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