#77 Side Door Trim Buckling

Here’s another nuisance trim problem that is common to these cars.  The ends of the side door trim molding are secured to the door with double sided adhesive tape.  Over many years the tape can come loose where the end of the trim will pull away from the surface.  Then when the door is opened the end of the trim jams against the sheet metal in front of it and buckles the molding out of shape and the door won’t open fully.

Buckled door trim prevents door from opening fully.

Ideally I would have replaced the trim molding but they are expensive and the color may not match the rest of the car.  So I straightened the trim out flat as best I could in place and then secured the end back down with silicone adhesive.  Clamped the end against the door with the front door propped open while the glue set.  Turned off the door open light to prevent battery drain while the door stayed open.   Cleaned it up a bit so it looks OK now.  Not as lovely as a new part but passable and cheap.

Two clamps hold trim in place while adhesive cures.

After straightening and gluing end of trim back on.

I could have done a better job if I had removed the strip and flattened it on the garage floor, then applied adhesive more precisely.  However, I had little time and the result is good enough.

If you notice your trim coming loose at the ends, re-secure it before you buckle the trim. It’s a lot easier to do before it’s damaged and looks better.

$0

#76 Roof Trim Peeling

The metal trim on the side of the windshield that continues on to the back of the car along the roof line is coated with a dark gray plastic material. The coating cracks and starts to peel off due to heat, age, chemicals and UV radiation.  In this case, a large piece was very loose and made a racket from turbulence when the car was driving.  Daughter temporarily secured with duct tape until the car came home for Easter weekend for me to deal with.

Tape held coating in place to prevent loud vibration when driving.

This coating rarely lasts 10 years so all Volvo 850 owners have had to deal with this by now.  There are three typical solutions to this problem.  First is to replace the roof trim with new parts.  They are hard to come by and expensive when you can find them ($180 each side).  Salvage parts are unlikely to last long since time and environment are the enemy here, if you can find any that are still intact.

The next easiest thing to do is to remove all the plastic coating and just leave the trim with the metal finish.  Changes the look but it’s not the worst thing.  Some people actually like it this way.  Sanding the trim smooth and shiny improves the look.

What most people seem to do is to remove the old coating and finish it smooth, then recoat or paint the strips to look more like the original.  For now I just removed the coating with a utility knife but plan to sand and then apply a dark gray bumper coating spray when I have more time.

Removed coating carefully using utility knife.

All coating removed; looks OK but I will re-coat later.

Both sides were coming apart so removed coating on passenger (RH) side as well.

Roof trim coating comes off of all 850s after 10 years. Sedans have a lot more exposed trim without the roof rack on the wagon.

$0

#75 New Headliner

Here is the second item not done at home; windshield replacement was the only other item we paid to have done professionally so far.

As mentioned way back in #11, the headliner was a big problem sagging badly.  I temporarily tacked it up using special headliner screw pins and it has held up for over a year now.  But this temporary arrangement was unattractive and there has been a persistent odor that I suspect is trapped in the fabric and foam backing in the headliner so it was time to replace it.

Headliner temporarily tacked up using special pins.

The upholstery shop carefully removed dozens of screws, molding and other fasteners to remove the entire headliner.  On wagons this is a fairly large piece.  Fortunately this project car does not have a sun roof which would have made the job more complicated.

Then they stripped the old fabric and foam backing from the structural headliner fiberboard.  New foam was then glued on followed by fabric to match what was removed.  The headliner was re-installed in the car and secured as before with all the fasteners and molding and such.

New headliner looks and smells great now.

Looks great now and smells better in the car.  Once the glue odor dissipates it should be very pleasant.

This is a potential DIY job but it is fairly involved.  You can buy kits which include new fabric, foam and adhesive.  You still have to remove the headliner board which can take a couple of hours figuring out and risk breaking aged fragile plastic clips.  For the price I felt it was worth having a professional do the work.  One specialty headliner shop did not even accept the job because the car was too old and they worry about breaking plastic clips and such.

$173 at a discount upholstery shop

#74 Slow Front Oxygen (O2) Sensor, Code P0133

An old, slow oxygen (O2) sensor was indicated with a check engine light (CEL) and error code P0133.

There are two oxygen sensors in this car, one that does most of the work in front of the catalytic converter (Bank 1 Sensor 1).  The rear is mounted just after the cat and it serves to validate the front readings and monitor catalytic converter performance by comparison.

Oxygen sensors can last a long time but after 100K miles or 10 years they can’t be expected to keep going and are recommended to be replaced even if they are not misbehaving.  At 16 years old and 160K miles this sensor is long overdue.  The front O2 sensor is largely responsible for an optimal fuel/air ratio so often replacing an old sensor improves fuel economy.  Will have to see if that is the case here.

Since the front sensor is the critical one and these are expensive parts, I replaced only the front O2 sensor.  This is fairly easy if you know what you are doing but lacking instruction I wasted a lot of time figuring out how to unplug the sensor connector from the wiring harness.

Start from above by unplugging the O2 sensor being replaced and unclipping the sensor cable from the frame.

Sensor plug is unlocked by prying the red connector latch up.

The front O2 sensor is on the left towards the middle of the car.  The rear sensor is on the right, which I did not deal with here.  Reportedly the two sensors are keyed differently so it is impossible to reverse connect them.

Raise the car and secure on jackstands to work from underneath.  Finish unclipping the sensor cable so it is free to the sensor.

Front sensor is located just in front of the catalytic converter after the exhaust manifold.  Spray penetrating oil around the O2 sensor fitting for easier removal.

Penetrating lubricant helps free the tight sensor. Note wiring clip removed from frame.

Break the sensor free from the exhaust pipe.  A special 22mm (7/8″) O2 sensor wrench is helpful here but not required.  Once it’s loose the sensor can be screwed out by hand.

Special O2 sensor socket maximizes grip on seized fittings.

Compare old and new sensors.  The new one has anti-seize lubricant on the threads already.  Used an exact Bosch replacement part.  Generic or universal sensors are known to have troublesome wiring problems or be unreliable.

Old and new sensor.

Close up comparison of old and new sensors.

New sensor installed and tightened in using special socket wrench.

New sensor installed and cable secured to frame below.

Sensor cable reattached to frame and plugged back into the harness.

Sensor cable secured to frame above and plugged into connector (Automatic Transmission).

Sensor cable secured to frame above and plugged into connector (Manual Transmission).

Lower car back onto its wheels and it’s ready to roll.  Reset the error code and hope it doesn’t come back.  It hasn’t reared its ugly head again and the O2 monitor has finally gone ready.

By age and miles the rear O2 sensor should also be replaced at the same time but it is less critical and the monitor is not complaining about it and they are expensive so will wait until the ECM throws P codes about the rear sensor before replacing it.

$152 new front O2 sensor

Technical Notes:

Trouble Code Conditions

• The engine control module (ECM) continuously monitors the time (period 3.3 seconds) it takes for the HO2S to switch from rich to lean and back to rich again. If this time is too long, the engine control module interprets this as a fault in the front heated oxygen sensor (HO2S) and diagnostic trouble code (DTC) EFI-435 is stored (P0133).
• Before fuel trim starts the front heated oxygen sensor (HO2S) must be ready – it should be at operational temperature and have the correct output voltage. Monitoring of the heated oxygen sensor function starts approx. 3 minutes after heated oxygen sensor heating starts. Diagnostic trouble code (DTC) EFI-212 is stored if there is a fault in the front (P0130, P0131, P0132,P0135) or rear (P0136, P0137, P0138, P0140, P0141) heated oxygen sensors or their cabling that affects the output voltage from the front heated oxygen sensor.

Function
The heated oxygen sensor (HO2S) only operates above certain temperature , approx. 285°C . Normal operating temperature is in the range 350 – 850°C .
The heated oxygen sensor (HO2S) is heated electrically. One terminal is supplied with 12 V by the main relay, while a second terminal is connected to the engine control module (ECM). When this terminal is grounded, a current flows through the PTC resistor in the heated oxygen sensor (HO2S).
When the heated oxygen sensor (HO2S) is cold, the value of the PTC resistance is low and the current in the circuit is high. The engine control module (ECM) pulses the current initially to prevent damage to the PTC resistor. The resistance increases and the current falls and becomes continuous as the temperature rises. The heating period is short, approx. 30 seconds.
The heated oxygen sensor (HO2S) can be damaged if it is exposed to condensed moisture from the engine while the device is hot.
Heating of the heated oxygen sensor (HO2S) starts immediately the engine is started. When sensor temperature reaches 350°C it is maintained at a constant level until exhaust gas temperature at the front heated oxygen sensor (HO2S) and catalytic converter temperature at the rear heated oxygen sensor (HO2S) are high. This is to ensure that the temperature around the sensors is high enough to avoid water condensing onto them.
Both heated oxygen sensor (HO2S) terminals are connected to the engine control module (ECM).
When the engine is running rich, the oxygen content of the exhaust gases is low or zero. The heated oxygen sensor (HO2S) is then transmitting an output voltage of approx. 0.9 V .
When the engine is running lean, there is an excess of oxygen in the exhaust gases. The output voltage from the heated oxygen sensor (HO2S) almost drops to 0 V .
The change from high to low signal level occurs at the ideal (stoichiometric) air/fuel ratio of 14.7 kg air/1 kg fuel.
The engine control module (ECM) continuously uses the heated oxygen sensor (HO2S) signal to control fuel injection so as to maintain the ideal air/fuel ratio of 14.7 kg air/1 kg fuel.

#73 Secondary Air System Fault / Vacuum Leak / P0410

The check engine light (CEL) came on so I plugged in my handy OBD2 code reader and learned that the car was complaining about the secondary air injection system with code P0410. Secondary air system (SAS) is an emissions control feature that pushes air into the exhaust to increase catalyst heating and to help burn up hydrocarbons and carbon monoxide.

SAS faults are common on Volvo 850s and I have spent a lot of time working on it in my 850 sedan.  Not sure if all model 850s have this feature or just certain North American cars, but it seems to be widespread in the USA at least.  Of course this cropped up shortly before the car’s annual state inspection was due and I had to get it happy before then.

This time the fix was very simple: an aged, cracked vacuum elbow at the secondary air system (SAS) valve was leaking so that the SAS valve would not open properly.

Leaky vacuum elbow at SAS valve.

Elbow replaced; no leak now.

I replaced this vacuum elbow and all other vacuum line couplers in the SAS system.  While the others were not in such bad shape they were degrading and would have failed eventually.  The elbow at the SAS valve is particularly subject to stress since it vibrates constantly when the engine is running.

Replaced both elbows at SAS control solenoid valve.

Replaced elbow at vacuum supply (intake manifold tree).

Replaced both vacuum line couplers to vacuum check valve.

Reset the monitor and the problem went away and has stayed away.

Others have worked out a technical fix to fool the engine controller into thinking the SAS is working when in fact the pump is not running.  In locales where environmental regulations are more relaxed this may be OK but I have observed that it may affect the oxygen sensors and cause other problems or reduced O2 sensor life.  So I chose to keep the SAS running normally on both my cars.

From what I can determine, SAS operation is monitored indirectly by the oxygen sensor in front of the catalytic converter.  When operating at cold start (rich exhaust), the air injected into the exhaust system burns residual fuel so the O2 sensor will see a relatively lean condition. If it doesn’t see lean exhaust after several attempts it assumes the secondary air system isn’t working and sets the CEL with P0410 code.

Some SAS details:

The major components in the SAS are the air pump, air pump relay, SAS valve and the SAS switching solenoid valve.  Any or all of these can be defective and cause SAS issues.  In fact, on my other 850 all four parts had to be repaired or replaced.  Besides these major players the vacuum tubing, elbows and check valve can also cause problems, as we saw here.

The SAS valve attaches to a tube from the exhaust manifold.  The big hose from the air pump pushes air into the exhaust when the controller pulls a vacuum on the control tube.  Older SAS valves tend to stick open so that even when shut off by the controller they allow exhaust gases to pass down to the air pump.  This valve was redesigned years ago to close more reliably but can still stick open.  A stuck valve can kill the air pump by allowing hot exhaust gases into the pump which condense and corrode the innards.  A valve which won’t open (frozen or lacking full control vacuum) will result in the P0410 error code.

The SAS solenoid valve switches the vacuum from the intake manifold to the SAS valve when an electrical signal is seen from the engine control module (ECM).  If the valve fails to switch you will get a P0410 fault.  If the solenoid coil opens up or the connector is unplugged, you will get a P0412 code.  This is located above the radiator fan below the shroud.

The air pump pulls air from the intake and pushes it into the exhaust manifold through a [supposedly] open SAS valve.  Common failures of the air pump are when the SAS valve sticks open and allows corrosive moisture into the pump which will seize up.  The air pump is situated below the battery shelf.  Access for testing or work is accomplished either above or below.  From above you need to remove the battery and battery tray.  From below you need only remove the splash guard from underneath the engine.  I find it easier to get to it below but you are working upwards while laying on your back to do this.

The air pump relay switches the high-powered pump motor on and off with a low level signal from the ECM.  Newer 850 models have the relay attached to the pump while older models have the relay mounted nearby.  Relays can fail or have connection problems which cause the air pump to not operate.

$11 vacuum elbow kit

Technical Notes:

The secondary air system reduces the emission of hydrocarbons (HC) and carbon monoxide (CO) and heats the catalytic converter more rapidly after cold starting. When the engine is started from cold the SAS introduces fresh air (~20% oxygen) into the exhaust manifold in order to promote after-burning (oxidation) of hydrocarbons and carbon monoxide. This makes it possible to increase the injection period and retard ignition, increasing exhaust temperature and activating the catalytic converter more quickly.

The system consists of:

• Air injection pump (1) activated via the pump relay (2). The air pump takes fresh air directly from the air cleaner housing to avoid introducing dirt and water into the system.
• The secondary air system (SAS) valve (3) with its built-in check valve prevents exhaust gases being forced into the air pump.
• A solenoid valve (4) which controls the SAS valve using the negative pressure (vacuum) from the intake manifold.
• A check valve (5) to maintain maximum negative pressure.

The Motronic 4.4 MFI controls the pump relay and solenoid valve using separate outputs from the engine control module (ECM). The SAS is activated 20 seconds after the engine is started if engine temperature is between -12°C and +35°C. After that the system remains active for 60-100 seconds depending on engine temperature. If car speed is below 10 km/h after 20 seconds, only the SAS valve is activated. The air pump only starts when car speed exceeds 10 km/h and operates until the SAS valve is deactivated, regardless of whether car speed drops below 10 km/h.

The air pump starts when the SAS is being diagnosed (at least 10 minutes after the engine is started).