2007 XC70 ECM121B code when below freezing, 30711554 Topic is solved

[XC70Rider]

An hour later I removed the intercooler pipe connected to the turbo. For the first time I loosened the clamps between that plastic pipe and it's rubber hoses and removed only the plastic pipe. I re-installed that plastic intercooler pipe tight and snug.

Another thing I gave a shot is further tightening the top 3 and bottom 2 intake manifold mounting bolts. I couldn't reach the bolt hiding behind the thermostat.
....

Neither the rubber intercooler pipes nor the intake manifold gasket was leaking to cause the ECM-121B code. I installed new Reinz rubber hoses to the over the engine intercooler pipe. I also replaced the intake manifold & ETM gaskets. A new banjo bolt and new crush washers were installed on the manifold.



This code used to appear during every cold start when I first got it last May. After replacing the burnt vacuum pump, the vacuum pump switch that was stuck open, all vacuum hoses, and the MAF it was still running 7% lean but the code didn't appear again until the temperature dropped below freezing. Today it still only appears when the temperature is below freezing. When above freezing it runs 7% lean but when frigid outside it drops to 8% then throws the code. I replaced the rubber inercooler pipes and gaskets cause I suspected they weren't expanding as much in the frigid weather. Another factor is it runs leaner at highway speeds than when city driving or idling.

Idling in park with a warm engine the MAF flow rate is 2.8 g/s (10kg/hour) which is lower than average. The other sensors to calculate air loss are the MAP, ECTS, and ETM. I cleaned all connections on those sensors, replaced ETM gasket, and checked o-ring on MAP sensor.

I'm going to have a friend blow smoke into the air intake today. I'll then hook up VIDA and get LTFR, MAF, and Throttle angle readings while driving.

If no leaks are found then the remaining culprits are bad wiring, O2 sensor, or ETM. When I cleaned the throttle butterfly valve I noticed it would close very slowly. The nylon springs might need replacing. If so MrBrian please give me a lead.

Thanks for your assistance!

[XC70Rider]

Knowing a clogged fuel system can cause a lean code I cleaned out the entire system minus the fuel pump. Installed a new Mahle fuel filter, replaced filters, O-rings, and pintle caps on injectors, and threw in BG44k twice.

[XC70Rider]

Had a friend blow smoke thru vacuum lines and nothing came out. I clogged the ports on the 3 separate hoses I tried and smoke only came out the air snorkel via the front fender.

No vacuum leaks have been found.

[XC70Rider]

Found this old thread in the ETM forum which describes how the MAF adjusts the throttle plate by detecting temperature and humidity

1999s70 (George) over on Swedespeed posted the following which I hope you will find highly informative and helpful:

As one who is on his 5th Electronic Throttle Module (ETM) and 4th Mass Air Flow Sensor (MAF), I’d like to write of my experience with these, in particular noting the symptoms of their impending failure (so that you don’t suddenly find yourself with a stalling car as an 18-wheeler barrels down on you from behind), and also telling you how to replace the MAF yourself and save lots of $$.

The ETM issue is well-known among those lucky Volvo owners who have the 5-cylinder engine in models produced in 1999, 2000 and 2001. Like me . Volvo has extended the warranty on original throttle bodies, for up to 10 years or 200,000 miles, and that discussion has, I’m sure, been had many, many times and is beyond this post. In my experience, throttle bodies last around 70,000 to 90,000 miles, though I did get 118,000 out of my original one.

Background:

The air intake path, at least on a naturally aspirated (NA) engine, is as follows:

Air Filter --> Mass Airflow Sensor (also called the Air Mass Meter, or MAF) --> Throttle Body --> Intake Manifold

The throttle body contains a metal “throttle plate” that pivots along its diameter, allowing more or less air through. The car’s computer determines the plate’s position based upon, among other factors, engine speed and load, engine temperature, and accelerator pedal position. Within the throttle body is a “throttle position sensor” which, I understand, is nothing more than a strip of resistance film, over which the throttle place moves. Depending upon the location of the throttle plate’s edge, the electrical resistance through the sensor strip tells the computer the exact throttle plate position. Minor adjustments to this position are made by the MAF, which senses temperature and humidity. For example, hotter, more humid air has fewer oxygen molecules available for combustion (hot air less dense, oxygen displaced by water vapor), so the throttle plate opens slightly more than “normal” in this situation. If it did not, then you’d have less oxygen in the cylinders, which would either cause the engine to run “rich,” wasting fuel and possibly fouling spark plugs or catalytic converters, or the car’s computer would reduce the fuel charge into the cylinder, with a corresponding loss of power. More precisely, your car would perform noticeably different depending on temperature, humidity, altitude, etc.
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My 2.5T runs much leaner on cold dry days. In warmer months in ran only slightly lean. Do our MAFs detect humidity and temperature? If so then maybe the Bosch MAF I installed isn't detecting the humidity therefore allowing more air to bypass the throttle plate on these cold dry days.

[abscate]

That description is poorly written IMHO

The ECU determines throttle position but uses inputs from the MAF and other sensors. I do believe the MAF is temperature compensated , I don’t know about humidity. The Bosch data sheet would tell that

Once warmed up your ECU controls the mixture in closed loop using the pre cat Oxygen sensor as the diagnostic. If your car runs leaner in certain weather, something is wrong with it.

[XC70Rider]

I've been suspecting it could be the upstream O2 sensor so I've been spraying PB blaster on it lately. It appears some spray is making it into the exhaust. When I start the engine it smokes for ~5min.

How do you replace that sensor? With an open end 22mm wrench from above or below?

[abscate]

An open end will make a mess of it, don’t try.

I’ve got a “flare nut version “ of a 22 socket with a wide grip, and also , for total commitment , you can snip off the connector and put a deep impact socket , 6 point , on it.

I’m in MA weekly once semester starts, if you are game

[EngineeringBloke]

The Bosch MAF sensor detects air mass and air temperature in the intake pipe between the engine air filter box and the turbo.

When you look at the MAF from the air box side (after disconnecting the air box), you can see a U-shaped wire with a small cylinder on thumb shaped sensor - the cylinder on the wire is the electrical component for the temperature sensor.

The air mass flow is determined by the cooling of air passing over a heated film plate within a duct of the thumb shaped sensor. The sensor adds energy to keep the film at a particular temperature, and so can tell how much the air mass is cooling it. The temperature reading from the other part of the sensor is factored in.

Increased humidity requires greater energy to heat so will be factored in by the heated film requiring more power.

There is a video on this page showing the air flow through an internal S-shaped duct to the film sensor, and how any foreign matter should be deflected though a bypass.
https://www.boschautoparts.com/en/auto/ ... 0280218089

When I was cleaning my original MAF, I was focusing on the temperature element and missing the duct where the film place is housed. You have to get CRC MAF cleaner inside the duct as well, and assure time for it to dry when cleaning.

[abscate]

So let’s get this right. If humid air comes in, it cools the rim better because the heat capacity it’s of water is higher than it, so now the MAF overreports the. Air flow. The increased flow is useless to the engine because water doesn’t burn. But wait, humid air is less dense than dry air, despite baseball commentators claims to the contrary, but thi sdoesmt matter because the MAF detects mass, not volume. All good.

These effects are small , because saturated air is only 2% water by mass. I suspect none of these things correct, and in fact the closed loop OXS does the fixing,

Variation in fuel value of gasoline is about 4%, so no point in open loop measurements better than this.

[XC70Rider]

I cleaned the temperature element and the air duct on the original MAF with CRC MAF cleaner then re-installed it. I also removed the air snorkel off the turbo to check the O2 sensor connector. The connector appears to have gold prongs that had some white film so I sprayed it and it's pigtail connector with electrical cleaner. Wires on the pigtail connector weren't wrapped so I threw on electrical tape and wire loom.

After taking her for a ride on this frigid night I got the same results. P0101 appeared within every mile or two. The OEM MAF had the same flow rate as the Bosch replacement MAF of 10kg/hr.

Well at least I know it's not the MAF causing the code. No smoke came out and I replaced air intake gaskets along with all vacuum hoses so it's not leaking air.

The only items left to check are the O2 sensor, ETM and the ECM. I'll hook up VIDA to get results while driving. I'll also try and test the ETM using VIDA. As mentioned earlier the ETM valve was closing slowing and not fully closing.