Rodent damage and MAF ABS interaction

[mpaton]

I've just recently discovered this misfortune to my 911, and to the wife's Transit Connect.

 

We believe it's a squirrel (or worse, a pair of them). The Transit Connect got it's #2 fuel injector wires chewed right through, and that was simple enough to fix. I learnt that a soldering iron that runs on 4 AA batteries actually is worth having, and the biggest frustration was my own old person eyesight. It seems that 55 years of being short sighted makes one used to having good close in vision, and cataract surgery taking that away isn't always as great as it seems. Why can we have auto-focus cameras, but not auto-focus glasses.

 

Anyway, the first thing I noticed on the 911 (2002 Carrera, manual transmission) was after it moved a few feet, the ABS and PSM announced itself as being disabled. After a few more feet, there was a check engine light, which turned out to be a MAF fault.

 

Closer inspection revealed that the squirrel had climbed up between the catalytic converters, and gone to the right rear side of the engine compartment, and chewed on 4 wire bundles.

 

The 4 wires in the MAF sensor bundle were all severed

both O2 sensor wire bundles were chewed on, but apparently non severed (by inspecting after taking off the car). I haven't yet tested the heater continuity on these, but I will.

The 4th wire bundle contained 3 wires, and all were severed. I don't know the function of this 4th bundle, I'm hoping somebody here might.

 

The O2 sensors each have plug and socket disconnects, and these physically mount to plastic clips that are part of a plate attached to the body of the car. this plate also retains a 5 wire connector

containing 3 pins with wires attached (and these 3 wires are severed) However, it looks like in the case of this connector, the plug is merely retained by the plastic plate, but there is no electrical connection to anything, at least on my car. Does anyone know what this connector would be for?

 

I imagine that when I repair the MAF wires, I'll be able to clear that code, but I still need to find the cause of the ABS/PSM failures.

 

The speed sensor wires have all been checked, and have NOT been chewed on. An Autel scanner that I have can display wheel speed on all 4 wheels, so that seems good.

As far as I know, all the other sensors for ABS and PSM are inside the car, and there are no signs that the squirrels have been inside.

 

I have not yet checked fuses, but but I intend doing that.

 

I believe that if ABS goes out, then PSM will always disable, but I don't know if the reverse is true.

 

Does anyone know if a MAF fault would also disable ABS? It doesn't seem unreasonable, but I don't know if it's actually the case. When I drove the car slowly, the short distance to my lift, it behaved fine despite having no MAF sensor, but that's not much of a surprise; reversion to an Alpha-N mode can work quite well. But I would think that Traction Control mode would want the airflow system to be fully operational. Clearly this IS wishful thinking, but I don't know if that's all it is.

 

I see, further forward on the right side of the engine  compartment what appear to be 2 large round wire bundle connectors, which don't look or feel chewed, but they are going to be much harder to inspect. I hope I don't have to.

 

Thanks,

 

Michael

 

[DBJoe996]

I have heard of cases where a faulty MAF sensor causes the ABS/PSM to malfunction.  Sounds like you headed in the right direction with fixing the wiring to the MAF sensor, and replacing it as well.  Do you have Durametric or a scanner to check for codes?

[mpaton]

I did buy a durametric early on, in 2002.  I'm not sure how useful that is, although it is the same year as the car.

 

Also the colors of the wires in the mystery bundle are

 

Purple/Green

Orange/Red

Brown

 

[akk65]

17 hours ago, DBJoe996 said:

I have heard of cases where a faulty MAF sensor causes the ABS/ PSM to malfunction.  Sounds like you headed in the right direction with fixing the wiring to the MAF sensor, and replacing it as well.  Do you have Durametric or a scanner to check for codes?

MAF fault can light up ABS and PSM warning lights because it is programmed so.

See: 

911uk.com - Porsche Forum : View topic - MAF Sensor - Is it Dead?

WWW.911UK.COM

---

911UK.com - UK Porsche 911 Resource Site & forum, Porsche Specialist, Insurance, parts, sales

 

[mpaton]

Thanks to both of you for this correlation between MAF faults and ABS/PSM. I don't have the wires repaired yet, as I've discovered the squirrel chewed the wire in 2 places, and after trimming the ragged ends, if I just joined them, the wires would be about 3 inches too short.

 

Anyway, I'm happy enough that it will probably work again when I fix the wires.

 

This is actually the second time I've seen the ABS/PSM warnings. I was just leaving the Porsche dealer in town, and it's site is elevated about 6 feet above the road wth a short ramp, so I was angling down this to avoid grounding the front cover, and was on the brakes until I could see the road was clear. Just as I could see the road was clear, the car went

 

Bong! PSM inoperative! Drive to Dealer

Bong! ABS inoperative! Drive to Dealer.

 

My thought was D***!!! why doesn't it know I'm already at the dealer. So I went out one entrance, and back in the next one. Turned it on and off a few times, but fault was still there.

Went in to talk to the shop foreman, and we reasoned that when I was going down the ramp, one of the front wheels was in the air, and as the brakes were lightly on, that wheel wasn't turning. When I came off the brakes, it was still in the air and the fault triggered before the wheel came down and started turning. Anyway the foreman came out, and when I started it up, the fault was gone.

 

Thanks again. I'll post when it's all together again. 

[JFP in PA]

You can lengthen damaged wires, providing that you use matching gauge wire sections, soldering the joints and then heat shrink tubing over the joints for water tightness and insulation.  Soldered joints are critical on many of the wires in these cars, and in particular those that carry low voltage signals like the MAF.

[mpaton]

I haven't driven it on the street yet, but the MAF and IAT in the MAF harness are working again, and the ABS/PSM is also.

 

I had intended to use soldered connections and heat shrink tubing and similar sized wires, and did so, although this practice always brings to mind being told in the late 70s, (by informed people) that crimping was way more reliable in the automotive environment, as the wiring could remain flexible, presumably due to not having stiff solder) and hence resistant to vibration induced damage. Maybe it's the greater availability of heat shrink tubing that makes the difference.

 

Thanks for the help.

 

Does anyone know what the mystery option not on my car could be? 3 wires, brown,  orange with red tracer, and purple with green tracer. connected to 3 female pins in 6 place inline AMP connector with BMW part number on it.

[JFP in PA]

3 hours ago, mpaton said:

I haven't driven it on the street yet, but the MAF and IAT in the MAF harness are working again, and the ABS/ PSM is also.

 

I had intended to use soldered connections and heat shrink tubing and similar sized wires, and did so, although this practice always brings to mind being told in the late 70s, (by informed people) that crimping was way more reliable in the automotive environment, as the wiring could remain flexible, presumably due to not having stiff solder) and hence resistant to vibration induced damage. Maybe it's the greater availability of heat shrink tubing that makes the difference.

 

Thanks for the help.

 

Does anyone know what the mystery option not on my car could be? 3 wires, brown,  orange with red tracer, and purple with green tracer. connected to 3 female pins in 6 place inline AMP connector with BMW part number on it.

 

Your hypothesis about crimping being better is dead wrong.  Soldering is always better for a simple, often misunderstood reason; resistance in the circuit.  Crimp connectors add a different thickness material (often aluminum) to the electrical circuit, and that can have huge implications to what happens next, especially sensor circuits like the MAF.

 

Equal lengths of twisted copper wire and aluminum tube have different inherent resistance when measured a very low ohm levels.  This changes the voltage levels sensor's see under the exact same conditions, the lower the voltage level, the bigger the impact.  Add in that crimp connectors add dissimilar metal and the possibility for corrosion to develop, further altering the electrical properties of the circuit, and situation gets even worse.

 

We had a car in the shop with complaints of repeated stalling for no reason while sitting at a traffic light or stop sign.  The warmer the engine was, the worse the problem. We went all over the MAF sensor and harness, looking for something obvious, but found nothing that jumped out at us.  While reading the car's PID values at idle, we noted that the MAF voltages would suddenly change slightly for no reason, and the engine would stall. Changing to our shop "sample MAF", it did the exact same thing, so it was not the sensor itself.  We disconnected the MAF harness and tested it for continuity, and it was fine under all conditions.  But when we tried looking at each wire for very small changes in resistance when the harness was moved or subjected to hot air from a heat gun, two circuits saw the resistance jump very slightly.  We cut the harness open and found those two circuits had small crimp connector repairs in them, both of which showed slight internal corrosion against the copper wires.  We cleaned the wires, soldered them, and heat shrink covered the repairs; problem totally disappeared, and has not reoccurred in more than four years of daily use.

 

Sensor circuits, particularly low or factional voltage signal circuits like the MAF, O2 sensors, temp sensors, etc., act totally different when very slight differences in resistance appear in the circuit.  On these, solder and heat shrink are the ONLY viable repair methods.