99 S70 Base - P0172, P0171 and P0174

Post by **E Showell** » 06 May 2015, 14:25

Recently replaced the throttle body with a XeModex refurb. I am now getting a P0172 (edit -- later picking up P0171 and P0174 as additional codes) code. Usual suspects seem to be vacuum leaks. I can definitely say the elbow on the power steering pump end of the intake manifold is connected and I don't believe there are any vacuum leaks. Over the past couple days, the cooling fan has stayed on post shut-off for about five minutes. It has been hot and humid c. 80 degrees F, but not exactly sweltering. Front O2 sensor was changed within the last 40 k miles and the ECT was changed within that approximate mileage. Slight rough running and cooling fan run on lead me to suspect bad ECT, although I have not had any hard starting issues.

I checked front O2 sensor voltage (via Torque) with the car idling and it was hovering around 0.5 V, rear sensor was fluctuating between 0.14 V and 0.83 V, but switching between values close to those at a seemingly regular interval.

Anybody else think this is a bad ECT?

Post by **misha** » 06 May 2015, 14:36

Because of cooling fan staying on after engine is switched off....i vote for bad ect.Oem is made by Valeo.Only aftermarket replacement that can be used without problems is Vernet.Nothing else.

I'm a bit concerned about rear o2 readings which should be steady or have very little fluctuation.Those readings you have indicates that your cat isn't doing it's job.

Your rear o2 sensor behaves like it's front o2.Your front o2 should behave like rear and rear like the front one.

Post by **E Showell** » 07 May 2015, 12:46

Here's a new wrinkle. Courtesy of one of the forum moderators who I met today, I had a higher end scanner on the car and pulled some live data from the MAF. Reading at idle was fluctuating between 5.5-6.5 gr/sec. At around 2000 rpm fluctuation was between 10.5 and 15.5 gr/sec.

It also pulled codes P0171 and P0174 in addition to the P0172. Is this data suggesting a bad MAF?

Thoughts?

Post by **abscate** » 08 May 2015, 03:34

Noodled a bit on this one. A fluctuating MAF reading could be either a bad MAF or a vacuum leak...either one could cause that. Swapping the MAF for a known good one is probably the way to test for which one you've got going on (hopefully not both!)

Post by **E Showell** » 08 May 2015, 04:05

I was doing some reading on another Volvo forum -- I know, the shame -- and ran into a post by a guy who had ETM issues and theorized that a bad ETM can take down a good MAF and that, indeed, an otherwise good MAF would likely fail very shortly after the ETM failed.

Post by **precopster** » 08 May 2015, 05:13

A bad MAF can give false throttle codes; that's why XeModex's fault tracing flow diagram asks if there are also MAF codes. The Boschs have about a 10 year lifespan. Densos just seem to chug along.

My Denso 2000 car recently gave a P0172 about 8 or 9 times.
I swapped the MAF at the time and it persisted. It then disappeared about 6 months ago.

I've replaced quite afew Bosch MAFs and here on the forum there are literally hundreds of failed Bosch MAF posts.

I've read of only one failed Denso MAF here on Matthews.. Having said that I'm not about to throw away my spare.

Post by **E Showell** » 08 May 2015, 05:39

It is a Denso unit and has been replaced before under the prior owner's ownership. Didn't realize those were throttle codes. I though they were O2 sensor codes. I'll swap in a known good MAF from another car and see if the codes disappear.

Post by **precopster** » 08 May 2015, 06:34

P0172 is not a throttle code. It's a lean air circuit code which can be caused by a number of things including O2, MAF, air leak.

I was merely highlighting that if MAF is faulty you should get throttle codes as well.

Post by **E Showell** » 08 May 2015, 06:55

Here's some more data from Torque Pro -- O2 volts -- Bank 1 Sensor 1, 0.47V; Bank 1 Sensor 2, 0.39V (both taken at idle).

Bank 1 short term fuel trim fluctuating at idle between -7.03V and -16.41V

Fuel Trim Bank 1, sensor 2 - short term latest 0.78%; Bank 1 Sensor 1 Latest 2.34%;

Fuel Trim Bank 1 long term, latest -22.66%

Not really sure what these numbers mean.

Additionally, retested mass air flow -- idle c. 5.5 gr/sec., 1500 Rpm c. 8 gr/sec., 2000 RPM c. 12 gr/sec.

Any thoughts?

Response to Mike -- Steve's Autel 500 did pick up P0171 and P0174 as well. Those aren't showing on Torque Pro or my cheapie Actron scanner.

My gut tells me this is a failed ECT.

Post by **precopster** » 08 May 2015, 13:53

Do a battery reset by touching positive to negative and see if this gremlin goes away. This will reset baseline fuel trims.