CANBUS Questions

[Citroënbender]

I’m still battling with the naughty Pug 307.

Among the faults it throws somewhat at random, is a complete loss of (electric) steering assist. Highly dangerous when you’re entering a small roundabout at 45km/h.

I’m trying to work out if the fault lies in another module as the transmission logs an intermittent fault for loss of CANBUS signal.

If I physically unpick the two bus pins from the steering module connector on the harness and insulate them out of the way, everything else on the bus (eg brakes, dash cluster) should still work pretty much as normal, right? I don’t believe it’s a terminating node. Hence this particular question.

Troubleshooting the steering is a bit difficult because I don’t have a pinout for the connector or access to its parameters. So I want to see if it has an inbuilt limp mode for no CAN data or if it defaults to no assist immediately.

[russellw]

What is the DTC it throws becasue I can probably get you diagnostic subroutines for the DTC given the global PCED applies across all OBD2 compliant systems.
I can probably dig up the pinout for the EPAS connector if you give me the year of the 307.

[Citroënbender]

It’s a 2004 model 307, the EPAS has a two pin power plug for the pump, and a nine pin socket but I think only five are populated on the harness - presumably 2x CAN, +12V, GND and a diagnostic line. I’ve got cracked software that is pretty good for the most part but it doesn’t have any dialogue with the module, even if I try diagnosing as another model.

Normally when the EPAS fails on these, it’s due to internal leakage and the multi pin connector drips with fluid. This one is decisively dry.

These are the only screenshots I’ve saved. There’s a sticky (petrol) EGR which gives me permanent faults - easy to fix, just need a round tuit - and intermittent failure mode on both transmission (default to full hydraulic) and EPAS. I swapped TCMs (they’re external and not hard coded) with no change.

I’m not sure how the fault code of “87” crosses over to universal codes.

Also I’m suspicious of the way this fault is reported, I’d have thought a loss of brake module data would show up as a VDC fault or loss of speedo but it never does.

There’s one post on MHHAuto with a matching fault, but no clear resolution (only advice was to clean the ABS connector, true for damp climates), and the OP doesn’t say if he had steering issues. So I can’t say if my steering problem is simply happening because it’s downstream of another fault, or is a self-contained failure.

[russellw]

From what I have available the 87 faulty code relates to the vehicle speed input from the ABS module on the CANBUS has no signal.
I'd suspect this could be an ABS wheel speed sensor intermittent fault or something else in the ABS system.

[Dr Smith]

This is all above my head but it was interesting reading both issues and possible solutions.

[ozpacman]

Originally Posted by Dr Smith

This is all above my head but it was interesting reading both issues and possible solutions.

I thought it must have been a couple of blokes from Mozambique having a yarn in their native Swahili!

[Dr Smith]

Originally Posted by ozpacman

I thought it must have been a couple of blokes from Mozambique having a yarn in their native Swahili!

[Citroënbender]

Short answer was/is - I don’t think it’s a terminating node. I was able to read other modules with the CAN wire pair (fairly sure pins 3 & 9 by ID numbers printed on the wires) unpicked from the EPAS connector, a struggle in cramped quarters. Default mode with these wires off, was zero assist - not full assist. I’m actually surprised by that.

Plug is populated in 1,3,4,5,6,9 only

@russellw: ID of a compatible unit (actual module is wrapped in a soundproof “pod” so the labels aren’t visible). I’m still keen to know the pinouts for this series of units, they also appear the same basic design as many of the aftermarket hot rod kits. Manufacturer is KOYO/HPI, now JTEKT and HPI.

Faults were able to be read with the plug fully re-populated and a loose connector in the OBD port remedied. A subsequent keyword search found one repairer discovering a plethora of dry joints in a similar unit. You wonder about durability of a repair without knowledge of why the joints failed.

[russellw]

This is all I have on the steering system covering 2001-04





In the diagram: 2=Ignition switch; 62 is the PS pump; 43 is the diagnostic socket; 42 is the ABS control unit; 3 is the main fuse box and 28 the SW switches.
Hope it helps.

[Citroënbender]

That is brilliant, thank you.

It’s really squinty territory - especially with a migraine on top - but the header pin for contact 5 looks to have a dry joint (too fine for a photo). As your diagram shows, that’s the switched Vbatt infeed which is a good reason for it to both shut down abruptly as it has been doing, and also be a likely fault due to current loads.

Have reflowed the header line for both nine way connector and the sub-board connector. Fingers crossed!

[aussiblue]

especially with a migraine on top

Most froggie cars will do that to you eventually.

[Citroënbender]

Unfortunately it looks like the fault is an upstream issue, likely in the ABS as mentioned. A twenty minute test drive brought back EPAS and transmission faults pretty much in unison.

The brake module has two CAN pairs, one goes to the transmission (and I believe steering), the other (primary) goes back to the motor, BCM, dash etc. As the brake module logs no faults but has full comms I think it’s likely the fault is a basic physical one like unbonded wires internally to the secondary CAN pair. A bit of heat buildup and connection drops out. A physical fault in the external wiring would be more susceptible to triggering by harsh road conditions.

However, I thought it worth sharing a few pictures (apologies to DFB for the grime). The steering’s a well built unit and if one could create a basic CAN input the assembly is easily adaptable to almost any car application.

[russellw]

Here is the diagram for the ABS system. 42 is the ABSCU; 43 the diagnostic socket; 44 is the brake fluid level switch and 45-48 are the wheel sensors.