After spending a lot of time in my local workshop for various jobs, my mechanic returned my 2006 XC90 V8 to me with a slight misfire which wasn’t there when I took it in. They were unable to track down the fault and the only 3 codes stored were:
– misfire detected, cylinder 8;
– coil H, primary and secondary circuit;
– system too lean, bank 2.
The misfire seemed only present at idle or under light throttle loads, possibly pointing to that lean AFR code.
Whilst waiting to get it booked in with a Volvo specialist, the situation has degraded significantly. I now have a near permanent misfire on cylinders 2 and 4 and a huge list of DTCs relating to many different systems in the car and I’m starting to get quite desperate, so any help/thoughts/guidance you guys can give would be greatly appreciated. I’ll list the work done below, the symptoms which led to the work being carried out, then the faults I currently have and, finally, my working hypothesis for the root cause.
Background and work to date:
Initial issue: failed accessory belt pulley, throwing the belt and damaging the timing case
Work done: replacement timing case, including relevant seals, and replacement belt & tensioner
Subsequent issue: significant oil leak
Work done: remove timing case, reseat seals and refit
Subsequent issue: message “power system service urgent” whilst driving, dead battery, oil leak still present
Work done: alternator tested @ 14v, battery tested and deemed dead, battery replaced, timing cover and seals reseated, crankshaft seal replaced, lower engine mount replaced, injector o-rings replaced, inlet manifold rubber gaskets replaced (however, steel gaskets looked tired to my untrained eye)
Subsequent issue: aforementioned cylinder 8 misfire
Work done: ignition coil replaced, wiring continuity checks, clean/reseat earth points
And that brings us up to date. The message I see most is “slow down or shift up” which I’ve seen before when a coil pack died on my V70, so I expect it’s generic. I also occasionally see “anti-skid service required”. I’ll list the codes I’m seeing, with any info I know about them, and then present my hypothesis.
Fault codes and best guess as to what they mean:
U3003(16) and U3003(17): headlamp control module (HCM) low voltage (<9v) and high voltage (>16v)
U0129(87) and U0126(87): HCM no communication with brake control module (BCM) or steering angle sensor (SAS)
B1D67(16) and B1D66(16): left and right HCMs signal too low (low voltage again)
P2303(16): ignition coil B primary circuit too low (cylinder 2 ignition coil low voltage)
P2987(2C): no description found
P2287(2C): injector control pressure sensor circuit intermittent (injector/cylinder number unknown)
P166C(C1): no description found, poss. MAF out of family
P216C(9D): fuel injector group E supply voltage, circuit high (high voltage, presumably >16v, not sure what group E is, poss. cylinder 5)
U3F9D(66): no description found
P101B(59): no description found, poss. MAF again
P0961(62): differential electronic module (DEM) pressure control solenoid A (AOC – mechanical clutch) reading out of range – suspect this is causes the anti-skid message
P0744(00): transmission control module (TCM) torque converter clutch solenoid circuit intermittent
P0304 and P0302: misfire detected cylinder 4 and 2
I’m sure I also saw somewhere in the OBD-II app that it’s running “open loop” which I assume is some kind of safe mode when it doesn’t trust the readings from the MAF and O2 sensors (closed loop). I also noticed different cat temps between the two banks and different voltages from the O2 sensors, presumably as a result of unburnt fuel from bank 2.
Hypothesis:
The battery was not the root cause of the “power system service” message, but was just another symptom/victim. Really it’s the alternator/regulator throwing shonky voltages everywhere and the quick multimeter test didn’t show it, or it’s simply worse now than it was. Or are all of those undervolt codes just because it’s idling between 350-400rpm and not spinning the alternator quick enough?
Thanks for reading through my ramblings and for any insight you can provide.
Ed.