Fault Context
Check Engine Light (CEL) came on possibly during return leg of a short ~8 mile total round trip around town (<35 mph) on very warm (86 deg) day with a longish stop midway (maybe an hour or so baking in sun including moving car once a short distance to move from one store to another). This trip was in the heat of the day. I wasn't the operator for this event, so the details, including exactly when CEL illuminated are sketchy. I found the CEL when the car was returned to me at home and it had been noticed at some point on return drive. After garaging it and lifting hood to check oil level (which was within limits) I noticed the fan on the ECU enclosure near the coolant and power steering reservoir was whirring. I haven't ever noticed that fan before, but it may be unrelated and just due to heat of day. Not sure. It doesn't often get that warm around here except in summer. Once car cooled in shade it was fine and hasn't repeated days later.
General History
2006 XC70, > 130K, 3rd owner, ~5 years ownership. It seems like car has been pretty well cared for with all the owners, and I've been doing my best to give it what it needs as things come to my attention since buying it. Car was within the recommended oil service interval for mileage, but it was time for a change despite the mileage. We haven't been using it as much because our driving patterns changed significantly during early stages of pandemic but are starting to ramp up a bit now and we are getting cars back to their pre-pandemic maintenance schedules.
Diagnostic and Repair Effort
Day 0 + 1: Initial Attempt: PASS
- Pulled codes with very inexpensive reader (HyperTough HT309). it showed a freeze frame reporting it had been logged by P0027 after about 800 seconds of engine run time. P0027 listed 2x plus P0079.
- Thought about problem and did some research here with car garaged.
- Replaced oil filter with "sacrificial filter", that I'm planning to swap out on short order to get any residual out of engine ASAP.
- Turned engine over. <1 min run time. CEL still illuminated.
- Replaced oil with Castrol Edge 5W30 High Mileage Full Synthetic.
- Turned engine over, <1 min run time. CEL still illuminated.
- Turned car over, CEL still illuminated.
- Took out for a drive. (Its cooler and overcast today and still morning.)
- Paused and attached reader ~0.1 miles into drive. Now it reports P0027 x 2 but P0079 is absent. Is this weird or expected?
- Cleared codes. CEL went out.
- Continued on to a gas station (~1-2 miles). Parked. Turned engine over. CEL stayed off.
- Filled up. Turned engine over and drove home.
- CEL still off at time of parking car. Fingers crossed.
- Later today, I may take a longer test drive commensurate with one that first triggered fault.
I decided to do an extended road test in heat of day to duplicate conditions that triggered the initial CEL described in "Fault Context" section before declaring victory. Car was reporting 84 deg F ambient and the sun was out in full, so this test was a very similar summer day as when the initial fault was triggered. Reference [1] below supports the temperature theory stating "A failing solenoid can give accurate(ish) readings when cold so i suggest to measure warm engine. Resistance goes very high then and eventually it's infinity."
- Pulled out of garage drove car about 10 miles around town, stoplights, local "country" roads (< 35 mph). No problems. No CEL.
- Parked for 2 minutes with engine off.
- Started engine drove ~100 yards to new spot. No problems. No CEL. Engine off.
(Maybe the engine took a bit longer to turn over or the CEL stayed illuminated a bit longer than normal at engine start. Can't be sure) - Paused in 2nd spot full sun with engine off for ~10-15 min. Possibly less.
- Start engine. CEL illuminates at engine start. Now only P0079 x 2 appears. P0027 is not triggered
- Cleared code, Drove 3 miles to stop point. Engine off. Noticed ECM box fan is running again. Paused there for a few minutes. Probably less than 15.
- Started engine, triggered another P0079 shortly thereafter. Made way home. Disappointed and thinking on next steps.
Day 2: More troubleshooting and Extended afternoon road test: PASS
- Pulled solenoid and valve body. Bolts turned very easily and body came off cleanly. Gasket seems undisturbed. Some light varnish on inside. Not too bad. I know I should replace the gasket, but I still want to figure out what caused this fault and don't want to use up gasket if solenoid is about to fail..
- Measured impedance cold at something less than 20 Ohms. Darn it seems like the original solenoid may be OK. Maybe I shouldn't have pulled it? I tried to measure this while on the engine but it was too hard to find the pins while they were pointing toward firewall (a spare connector with wires would have been handy here! Oh well.
- With solenoid facing up and valve body facing down I sprayed a very small amount of cleaner on body and let it drain out and dry
- The "veins" on top of valve cover did have some oil accumulation that looked a bit dirty (much dirtier than oil on dipstick right now. I soaked some of that up and cleaned up the surface of the gasket by dabbing up any oil that was on it from when the the valve body was pulled off. The gasket was firmly affixed to engine. The top side of the screen on the gasket looked reasonably clean and clear. The bottom side could not be seen given the gasket was affixed to the engine. I decided to reattach the original solenoid and see what would happen as an experiment. I was disappointed to find the solenoid was reading low resistance after I had pulled it and am now thinking it may be fine (at least for now). Maybe the screen just needs unplugged by applying a new gasket? Who knows?
- Re mounted solenoid and valve body on engine, tightening bolts in star pattern to 60 inch pounds.
- Cleared codes and turned engine over. All good. Let it warm up and RPM drop from around 1500 to 600-800.
- Turned engine off. Checked gasket. Very small, almost imperceptible, amount of oil had leaked out toward the outboard side of the engine and timing belt. It seemed to mostly be a light film on the top of the valve cover where it lips out toward the cam sprockets. Cleaned up the little bit of oil. Gave the bolts another 1/8 turn.
- Turned engine over again. Same process. Let it warm up until it was idling stably at 600 RPM.
- Checked for oil around gasket. All clean. Engine off,
- One more engine cycle. Repeated glove test. All good, glove sucking into oil fill port. Engine off.
- Did a 20 mile round trip, mix of around town and highway driving. Dash reporting 86 deg F ambient. Same weather as day 0 when failure was encountered.
- Hmm. No problems, No CEL. MPG seems typical given mix of highway and around town. Failure seems intermittent.
- Parked car. Engine off for 2 minutes again.
- Started car, drove another 5 miles around town. No CEL. No problems.
Still need to decide on next steps now. Have a new exhaust solenoid and gasket in hand. For the moment the error seems to be cleared, so I guess its a wait and see process then to see if the CEL is triggered again or the solenoid totally fails. Any other ideas or suggestions?
Still agree with sentiment that better diagnostic tools could help here.
Needs:
- Socket based probe kit. What are diameter of solenoid pins? See: https://probemaster.com/pin-socket-flexible-adapters/
- Alternatively, get a spare VVT solenoid connector to use for checking resistance of solenoid. Ideas for where to buy these?
- SKIP: Check fuses? Its working now, so it can't be a fuse. See https://www.swedespeed.com/threads/cel- ... st-4746345
- DONE: Reference [1] indicates Expected: 3.7 ohms. Failed: measures 25K ohms.
- TODO: Verify replacement part is working (Some folks report faulty replacement parts lead to confusion about faults)
- TODO: Remove and replace exhaust cam solenoid: Either torque bolts to 60 or 84 inlb per info in this link
viewtopic.php?p=415974#p415974
- Solenoid failure temperature theory https://www.swedespeed.com/threads/p007 ... ss.330801/
