1995 855T Failing Cat

[Klausc]

My project car is doing very nicely, thank you. I replaced both O2 sensors when the front sensor started to fail. Now, when I drive slowly, as in bumper to bumper traffic, I get code 4-4-3 = cat converter efficiency low. After only 187K miles? This doesn't happen while cruising in 4th gear. And no rotten egg smells.

Minnesota does not inspect cars. So, I was wondering if a spacer for the rear O2 sensor would trick the system into thinking all is OK. I am just tired of clearing the same code.

Thanks.

[Ozark Lee]

It should. Where you get in trouble is when the converter comes apart internally, when that happens the back pressure is pretty huge. So long as it doesn't sound like it is full of gravel it should work fine.

...Lee

[Klausc]

Thanks Lee.

[RickHaleParker]

4-4-3 ≠ cat converter efficiency low.

4-4-3 = ABS/TRACS Pump motor. Electrical or mechanical fault

Condition
If the control module finds that the voltage from the pump motor rotation sensor is missing after approx. 0.2 seconds when the control module trips the pump motor, or the control module receives a signal telling it that the pump motor is continuously on without being tripped, it posts DTC 4-4-3.

Substitute value
ABS/TRACS cuts out.

Possible source

• Signal lead to combination relay pump motor relay short-circuited to ground or supply (terminal 13 on combination relay).
  Open circuit in signal lead to combination relay pump motor relay (terminal 13 on combination relay).
  Open circuit in pump motor ground lead (terminal 2 and 3A on combination relay) or supply (terminal 1A and 15 on combination relay).
  Pump motor supply short-circuited to supply (terminal 1A on combination relay).
  Open circuit in rotation sensor signal lead (+) or signal lead (-).
  Rotation sensor signal lead (+) or signal-lead (-) short-circuited to supply or ground or short-circuited to one another.
  Faulty combination relay.
  Faulty rotation sensor.
  Faulty pump motor.
  Contact resistance in terminals.

Fault symptoms
With some faults, pump motor may run continuously without being tripped.

[Klausc]

Oops. I forgot to say the error code was from A-2. Yes, there are ABS codes, but they are in A-3. Most ABS failures will light up the ABS/TRKS lights, not the CEL.

Nice to have fender mounted OBDI rather than a dumb scanner (which I have).

[RickHaleParker]

Code A2 4-4-3 (TWC Efficiency)

1) Check for other codes. If any code for misfiring is stored
(Codes 4-5-1, 4-5-2, 4-5-3, 4-5-4, 4-5-5, 5-4-2, 5-4-3, 5-5-1, 5-5-2,
5-5-3, 5-5-4, 5-5-5, 5-4-4 or 5-4-5) perform that testing first. If
Codes 4-3-5 or 4-3-6 are stored, perform testing for that code first.
If none of the above codes are stored, go to next step.

2) Perform a compression check on all cylinders. Repair as
necessary. If compression is okay, go to next step.

3) Check for air leakage in intake system. Repair as
necessary. If there is no air leakage in intake system, check for air
leakage in exhaust system. Repair as necessary. If there is no air
leakage in exhaust system, check fuel and residual pressure. Repair as
necessary. If fuel and residual pressure are okay, retest using new
TWC.

[gmh]

The quote below is from this thread:
viewtopic.php?f=1&t=49901
I had the 443 issue as well on my 94 Turbo and solved it with a spacer. It passed emissions the next year and burned a valve in 10/13.

[quote="matthew1"]P0422 has been bedeviling me and my 850 for some time. I can tell you what it's not: it's not my 850's cat, it's not rear O2 sensor, and it's not the gas cap. If these attempted remedies aren't logical, it's because I was getting a sporadic P0440 also, and I was hedging my bets.

[list][*]Cat: I passed emissions after much procrastination and nail-biting. The numbers were very good. With a failed or failing cat, the numbers would have been awful. On my street coming home, I got a CE... P0422 again .
[*]Rear O2: I tried to defeat the code with a new sensor. No luck. At least I won't have to change it for a few 10k's of miles.
[*]Gas cap: New gas cap, still getting 422.[/list]

I too have had issues with the Cat efficiency code, but on my 94 850 Turbo the code would only show up in the OBD1 box as 443 in the A2 port. I could tell that the code was set without checking the ODB1 because it would reduce the turbo boost by about half. Strangely the CEL would never illuminate(I knew it was not a faulty light because other CEL codes such as knock sensors would turn it on), but the code was always present in OBD1. Also, I could clear the code with either OBD1(tedious to do all the time) or through the OBDII port with my cheapy scanner.

After replacing both O2 sensors which had over 100,000 miles on them the problem persisted. I was also convinced that it was not the Cat because it always passes emissions tests by miles. Thanks to the discussion in this thread https://www.matthewsvolvosite.com/forums ... 22#p226122 between Matthew and Justin, I found the fix. A $6 (Ebay) O2 spacer on the rear O2 sensor has kept the code away for months. As Matthew mentions in the thread, there is not much room and the one I got was barely an inch long and just fit. I know this is cheating, but it was a constant annoyance having only 1/2 boost. Hopefully the emissions place won't notice it when it is due next! It is pretty well obscured behind the protective shield. FYI for anyone attempting this, the more expensive ($20) 90 degree angle spacers do not fit!

[abscate]

I’ve forgotten the physics of why the spacer works, anyone remember?

[RickHaleParker]

I’ve forgotten the physics of why the spacer works, anyone remember?

It is not physics it is data manipulation.
The spacer moves the sensor out of gas stream therefore reducing the sensor's sensitivity to oxygen in the gas stream. A spacer does not fix the problem, it fudges the data.