Mk2 Focus - Engine malfunction and acceleration reduced

[LTIronWolf]

Hi all,

My Focus started to misbehave today out of nowhere, and I’m asking in case anyone has any bright ideas.

I have a 2006 Focus with a Facelift cluster and retrofitted cruise control (both mods done by me), after my original cluster died because of the classic pre-facelift problem. Everything was working fine with no issues, and I’ve had no bumps or accidents until I got into my car today to start the car. My cluster started to chime, displaying the messages “engine malfunction - acceleration reduced” however this was very intermittent.

The car alternated between not cranking at all whatsoever (dead silence when turning the key), succesfully starting but still showing warnings, or starting succesfully with no warnings whatsoever. I managed to drive the car home safely with no issues other than a check engine light on my cluster the entire journey home. 

I got home, and after failing to connect to my PCM using FORScan a few times, I finally managed to read the DTCs and all of them were related to CAN bus connectivity or signalling problems. I made a note of all the codes that were present, wiped the DTCs, and re-scanned to see if anything came up - all fine, no issues. The CEL also disappeared so I assume the car was all fine.

I went for a drive a few hours later, and during the drive all of my issues came back. The car started fine, but chimed about “engine malfunction” and “acceleration reduced” several times while driving. The cluster would also alternate between the rev counter and speedometer either showing their given values, or dropping to 0. When the messages appeared and the counters dropped, the cluster also showed a CEL, the ABS, oil, and battery lights - it’s like the entire cluster wasn’t communicating with the PCM. The exhaust was also making a deep raspy sound, and the car would occasionally judder, and the accelerator felt like it was stumbling and catching up.

Judging by the way the car was behaving and the DTCs I scanned earlier, it seems like the CAN bus is intermittently connecting somewhere, which seems strange as surely the car shouldn’t be able to work if the CAN bus is interrupted? I’ve had CAN issues in the past which I’ve written about previously here, but those were just due to physically loose connections. It has rained and snowed recently - could this have upset the car somehow?

Thank you in advance!

[LTIronWolf]

@Tdci-Peter You've been a great help to me in the past. Any ideas this time round?

[Tdci-Peter]

22 hours ago, LTIronWolf said:

Judging by the way the car was behaving and the DTCs I scanned earlier, it seems like the CAN bus is intermittently connecting somewhere, which seems strange as surely the car shouldn’t be able to work if the CAN bus is interrupted? I’ve had CAN issues in the past which I’ve written about previously here, but those were just due to physically loose connections.

Once running, the car can just about continue to work without the CAN bus. The ECU has all the essential information it needs to keep the engine running, The ABS and steering can work in a default independent way, which is an essential safety requirement as the CAN bus can not be regarded as reliable enough for safety critical operations.It certainly sounds like a major CAN bus failure.

Have you done the resistance test, 60 ohms across the bus when power is off. It can be done via pins 6 & 14 of the diagnostic connector. It needs to be done when it is in a misbehaving mood. 120 ohms would indicate a break in the bus between ECU & Cluster (PCM & IC in Ford terms).

Any water getting in to the footwells? This can accelerate corrosion in the connectors in front of the passenger door that carry the bus.

[LTIronWolf]

On 2/9/2019 at 7:38 PM, Tdci-Peter said:

Once running, the car can just about continue to work without the CAN bus. The ECU has all the essential information it needs to keep the engine running, The ABS and steering can work in a default independent way, which is an essential safety requirement as the CAN bus can not be regarded as reliable enough for safety critical operations.It certainly sounds like a major CAN bus failure.

3

That's interesting, I never actually knew that. Does the PCM connection count as part of the CAN bus? I can't imagine how the car would cope if the PCM were somehow disconnected or interrupted, hypothetically speaking.

On 2/9/2019 at 7:38 PM, Tdci-Peter said:

Have you done the resistance test, 60 ohms across the bus when power is off. It can be done via pins 6 & 14 of the diagnostic connector. It needs to be done when it is in a misbehaving mood. 120 ohms would indicate a break in the bus between ECU & Cluster (PCM & IC in Ford terms).

1

I have not, but after some testing I've managed to track it down to the cluster itself - always seems to be a problem child with Mk2 Focuses. It seems to be either the connector on the IC itself, or the harness connecting to it that is causing the issue. The problem tends to kick up when I'm driving, and it's very random when it happens. Sometimes it won't, and can even change states a few times in the space of seconds when driving. After poking and moving the cluster a bit while driving, that tends to either cause it to reconnect when displaying "engine malfunction", or it causes it to disconnect when it's running as normal. Leads me to think something isn't making proper contact.

When I tested the car at home, I unscrewed the cluster with the harness still attached and played with it while the car was running. I can't properly tell whether it's the connector itself that has bad solder joints or connections, or if there's a break in the wires in the harness that connects - I think it's the former. Is it common for the harness to break or misbehave? I'm going to reflow the solder on my IC connector and see if that fixes it. Keep in mind, this is a facelift cluster with the new layout and design, and was manufactured after the famous 2005 year clusters which were prone to breaking. Is it possible for these to have bad connections as well? I didn't immediately consider an IC problem as I figured the facelift clusters were much more robust than the original ones. 

 

On 2/9/2019 at 7:38 PM, Tdci-Peter said:

Any water getting in to the footwells? This can accelerate corrosion in the connectors in front of the passenger door that carry the bus.

3

Nothing that I can think of, no. The only water that could have possibly gotten in was during the snow 2 weeks ago, when I got into the car with traces of snow on my shoes. This would only be small quantities, and it should have melted into the carpet.

[Tdci-Peter]

22 minutes ago, LTIronWolf said:

Does the PCM connection count as part of the CAN bus?

All the engine sensors and actuators connect directly to the PCM / ECU. It gets power direct from the battery. So it only needs vehicle speed (from ABS), PATS authentication & back-up accelerator pedal sensor (from IC), electrical load & A/C commands (From the GEM / BCM / PJB) and a few other non-critical inputs over the CAN bus. It can keep the engine going in a basic, default way, without the CAN bus.

The Focus IC is a large pcb, with a single unsupported connector in the middle. I suspect the Mk2a IC is similar there. Vibration will stress the whole pcb, and stress the connector solder joints. The cable loom to the IC should be supported by a clamp near the back of the IC, onto some part of the facsia. Check your loom is adequately supported to minimise the stress the cable puts on the connector, and to damp down vibration. All solder joints are weak when continuously subjected to stress and vibration. It gets quite bad thermal cycling as well from sub-zero nights to direct sun on warm days. And humidity can be high, with condensation, as a result of these temperature swings. So it is in quite a tough location for such a large, important pcb. It is no big surprise that they sometimes give trouble.

All you can do is check it is all supported as well as it can be, after checking for cracked or dry solder joints.

[LTIronWolf]

23 minutes ago, Tdci-Peter said:

All solder joints are weak when continuously subjected to stress and vibration. It gets quite bad thermal cycling as well from sub-zero nights to direct sun on warm days. And humidity can be high, with condensation, as a result of these temperature swings.

 

I was thinking exactly this. Over the past 2-3 months, it's cycled from minus temperatures to 16C, and it's varied every single day - I wouldn't be surprised if that is what caused it to fail.

I reflowed the connectors on the back of the connector, and everything is fine again. I nudged and moved around the IC like last time to check that it's been fixed and everything seems to be fine. I've cleared all DTCs related to connections and I see how I get on over the next few days. Hopefully it stays away for good!