OBDII Data: Barometric Pressure

 The barometric pressure in my area was 30.18 so lets compare some cars. The 2009 Hyundai Elantra Barometric Pressure pid was in PSI rather than inHg so math, 14.5 PSI x 2.036 = 29.52 inHg. When you see about 14 or 15 on that pid you are seeing PSI. The Hyundai has an actual Baro sensor soldered into the printed circuit board of the PCM. We will call that 29.52 close enough. The Barometric pressure from the weather report is usually corrected to sea level so subtracting .3 would be the raw (what the car feels) pid. 29.88 inHg. A faulty Baro reading on the Elantra would cause a subtle shift in calculated load, and some related shifting concerns. 

   Lets take a look at the pid on the 2008 Chrysler 300C. The gold standard is met, 29.8 from the Chrysler Baro sensor, I believe it is also a part of the PCM on this model. 

Chryslers are big on logic, and rationality. When you turn the key on prior to start it will compare things, taking it all into account. For instance, since the engine is not yet running the MAP reading and Baro reading should match. It will monitor throttle position, map and baro once running to see that the readings make sense. It uses that Baro pid to calculate pressure ratio. If it sees something irrational it can go into limp mode, or disable the cylinder deactivation since it can't determine the load values. 

2000 Ford Taurus 3.0 DOHC: RED FLAG. 

The Ford is showing a Baro pid of 13.2 psi, or 26.87 inHg. Now the Ford doesn't have an actual Baro sensor. It calculates the Baro based on MAF sensor readings. Seeing the Baro off makes me suspicious of the MAF sensor. 

Interestingly enough the g/s of the MAF was 3.96 so slightly high but not alarmingly so. What seemed out of place is the long term fuel trim of 7%. Off into theoretical land, since the Baro pid was 26.87 perhaps the computer sees the higher altitude than actual and is using a fuel control strategy for "thin air". 

A quick wide-open-throttle gave me 104.4 g/s airflow before the rev limiter kicked in so lets clean that MAF and see what happens. It is not easy to safely reach that lower spool which would be the culprit but we'll give it a shot.

After cleaning i am idling at 3.43 g/s. Baro is now changed to 26.8. WOT is 110.79. Cleared the KAM and Baro went to 28. Time for the test drive. It may take awhile for the PCM to recalculate that Baro pid but it is headed in the right direction. 

TEST DRIVE: WOT load hit 95%. g/s airflow reached 127.35, LTFT is now 0, Baro is still 28 but it is just a slow learner. Major improvement.

Thanks for reading.

Kenny@GGAuto.Repair

 

1985-86 Audi 4000S Belt Adjustment

 

Scan Lab: AUTEL MaxiCheck MX900

 I was just going to post a brief run through using this MX900 on the Mazda CX-5 that is here with the A/C leak.  Bear in mind the system is empty and has a code stored for low refrigerant pressure, P0532. 

What I noticed in looking at the internal data for the front body control module is that the ambient (or outside) air temp was -40F which while it is cooler today than yesterday it isn't that cold. One nice thing about this tool is it will use the color red on a data item it thinks you should notice. So even the MX900 didn't think it was really -40 outside today. 

The ambient air sensor is in the front grill area and you will see a -40 as the default if the circuit is open so I looked but looks solidly connected. 

The PCM also monitors the ambient temp sensor so I wanted to know if it was also seeing -40 because that would affect engine performance, among other things. The only trouble code I had was the refrigerant pressure, the car runs and starts well and I had a feeling the PCM was not seeing -40 when taking all that into account. The PCM was seeing more logical temp from the sensor and no red pid. 

Now sometimes you aren't looking at the same data the PCM is seeing because it can make substitutions based on its reaction to an out of range sensor. So to be sure I was looking at the actual data pid and not an enhanced version I went out of the OEM data and entered the global (or generic) OBDII data which by law has to show the actual data, not enhanced. This was also normal temp.

Just what was going on here? Was this a problem internal to the front bcm? Was it a corrupted datastream that only affected one pid? I then noticed the "outside temp" displayed on the cluster was also normal. 

Now seemed time to study. On many cars the front body module would be feeding the outside temp display but I wasn't sure on this Mazda. If it worked that way here then the FBCM was very aware of the actual ambient temp but was defaulting to -40 internally for some reason. If the outside temp in the cluster was fed the data from the PCM or directly from the sensor then I was back to a data fault or an internal problem with the FBCM. Thinking about it and reading as much as I could come up with, this is what I decided. Whether the outside temp display relies on data from the sensor, PCM or FBCM I'm not 100% sure but I suspect the FBCM knows the actual sensor data but is altering the data internally to assist it in reacting properly to the low refrigerant. It isn't trusting the data but knows something isn't right so just defaulting to -40 and not dealing with A/C until it is fixed. 

It was simply refusing to accept ambient temperature data because the A/C system was empty and the refrigerant pressure sensor was reporting 0 psi.

Thanks for reading. 

Kenny@GGAuto.Repair

Scan Lab: Snap-on APOLLO D9

 Okay, 2018 Dodge Journey, with both temp controls set to coldest I have 47 on driver and 98 on passenger side. The 48 lets me consider that I have a good refrigerant charge. I want to look for codes. The TPMS has several that look like may have some failing tire pressure sensors. I did a clear on that and we;'ll see what comes back,. SCCM has a low voltage code but not addressing that yet either. What I don''t see is any HVAC code indicating a failed temperature actuator on that passenger side. 

I tried to command the actuator position and got no response. 

When I tried a blend door calibration the HVAC module finally noticed the actuator wasn't moving and gave me a trouble code. 

Replaced the actuator and did the re-calibration again with a pass. 

Next up the Toyota Sequoia that the A/C stopped working on. When you see the A/C flashing you can expect some coders are stored. 

The solar sensor codes are normal when the truck is inside out of the sun but that B1422 indicates the compressor is seized and yes, verified. Needs a compressor and condenser. 

Thanks for reading.

Kenny@GGAuto.Repair

Scan Lab: AUTEL MaxiSys MS906 MAX

 Gonna change things up just a bit and actually do some diagnostics this time. This 2013 Accord was here for a valve cover gasket but I also noticed a tire monitor light on. After checking the tire pressures and all were fine, I thought to enter the TPMS (Tire Pressure Monitor System) data and see what it had to say. I found this Accord has no TPMS. It doesn't even have tire pressure sensors. It uses the ABS module to calculate tire pressure as it monitors tire diameter changes. Now when you can look into TPMS data you can see how much tire pressure the system is reading from each pressure sensor but not so here. I scanned instead for codes in the ABS and found two, one said I had a tire with a different diameter in left front or right rear and I had a low tire pressure in one tire. I couldn't see which tire was "low tire pressure" as it has no data for that in the data stream. It also isn't clear about that left front or right rear though I suspected one of those triggering both codes. That VSA System Malfunction would probably be related to the ABS codes. VSA is the vehicle stability assist system which of course would be concerned with a wrong diameter, low tire. The EPS is the electric power steering module which also needs to know your wheel speed, so isn't trusting the wheel speed sensor of a tire that seems to be out of range and triggering these codes. Now I had checked all the tire pressures and they were fine. Next I wanted to make sure all the tires matched in size and brand, which they did. 

There is a bit of forensics involved in car repair so best I could make sense of the evidence was that perhaps this did at one time have a low tire, which could trigger all those codes, but the low tire had been repaired of filled and was no longer low. This would mean that perhaps the system simply needed to be re-calibrated which can be done via the central display in the car. Use settings, scroll to vehicle settings, then choose TPMS calibrate and re-calibrate. The car needs to drive some distance at beteen 30 to 60 mph and will reset. 

The low tire light went out and the codes cleared. All fixed. Previous to the calibration the codes would not clear but remained in permanent codes. 

Let's move on to the 4Runner with cat efficiency codes, P0420 and P0430. 

Now a cat efficiency code will usually set then a cat monitor is too active,. A fully warmed vehicle with a working cat should see the rear O2 slightly rich at 2000 rpms and fairly steady. If it is reacting to the fuel mix too actively the computer determines the cat isn't working properly and you get the code. But here if I look at the O2 monitor test results for each sensor I can see they are failing due to slow response time. 

Now when I graph the rear sensor signals I can see that I do indeed need cats. That bank 2 sensor is slightly rich and fairly steady all right but that isn't quite near enough to the 0.65 I would expect. The bank 1 is switch too much rich to lean though the activity is indeed slow. So far it looks like I need cats AND rear O2 sensors. If these rear sensors were working properly, as new ones will they will just more quickly say, hey these cats aren't working. 

Only one thing left to check. I want to see that the front O2 are showing me a good fuel mix going into the converters. Technically this 4runner is using Air/Fuel ratio sensors in front of the cats. You monitor these by looking at lambda. Lamda is 1.00 and lets you see if the system has good fuel ratio control as it stays near 1.0 with only very slight variations. We have good fuel control here. 

Thanks for reading.

Kenny@GGAuto.Repair