How (not) to use DTCs (check engine codes) to diagnose problems

I see a lot of misunderstanding of what it means when your “check engine light” (MIL: Malfunction indicator Lamp) is on and what the “codes” (DTC: Diagnostic Trouble Codes) mean. Let’s discuss this a bit in general terms that apply to most vehicles and situations. As with everything, there are always exceptions.

First of all, why does your MIL come on? It’s because the ECU has stored a “hard” DTC. This is an event which likely has happened many times and with sufficient severity that the DTC has gone from a “pending” state (which you can read with a code reader but does not illuminate the MIL) to a “hard” state.

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944 Parts Cross Reference

I recently tried to find this information with a bookmark I had set.  Apparently this site no longer exists, so I rescued the information from and figured I’d post it here.  This used to live at:

The following are a list of Porsche Parts and their common cross references.






944/951 Ref and Speed Sensors BMW
12 14 1 708 618
12 14 1 710 668


Visor Clips VW
3B0 857 561 BY20 . . . $4.68 . . . Pearl grey
3B0 857 561 BB41 . . . $5.01 . . . Black
3B0 857 561 B8YS . . . ($.?.) . . . Light Beige

For the clip-on dress cover:

3B0 857 563 BY20 . . . $1.70 . . . Pearl grey
3B0 857 563 BB41 . . . $1.70 . . . Black
3B0 857 563 B8YS . . . $1.70 . . . Light beige


Oxygen Sensor Ford Tauras 13913


Starter Advance Auto
951 Exhaust Studs / Intake bolts Saturn 11518152 Torx Tip
951 Fuel Pressure Regulator (FPR) 80’s BMW 5 series
BMW 13 53 1 711 541
Bosch 0 280 160 249
NAPA CRB219514 / BA 158024
Upgrade to 3 bar from stock 2.5 bar
944 Brake Pad Pins NAPA part # 82682 from a 1994 toyota T-100 pickup.

NAPA parts link
Bosch Cross Reference for all Bosch

For updates and comments,

If anyone would like to claim/maintain this, please feel free.  I’m just reposting it because it disappeared.

Fix and flip: The Saga of the 2000 S10, Part 11

Today is going to be some final motor work and some cosmetic work.

The cabin fan sounded like it had mice living in there when it was on, so I pulled it out to see if I could get at the bearings to lubricate them.  No luck.  It’s just not worth the trouble.  I picked up another one for $30 and replaced it.  It’s not terrible to get at as far as these things go.

You have to move the ECU out of the way (silver thing on the right), remove its mounting from the coolant expansion tank, the expansion tank itself, and the frontmost stud that the expansion tank mounts on.  Two of the bolts (towards the fender) are pretty terrible to get at, and this is yet another “SURPRISE!  We decided not to use metric fasteners here!” area.  For the fan itself only, of course (they are 15/64).  The rest of the things you need to take out are all 10 MM.

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Fix and flip: The Saga of the 2000 S10, Part 10

It’s been a long time.  Too long.  At the end of Part 9, I mentioned that I had cross threaded the crank bolt.  What happened there was when I used the steering wheel puller to remove the crank pulley mount, I didn’t leave the bolt in place (it doesn’t interfere with the pulley mount), and the threaded rod of the steering wheel puller mangled the first few threads.  In an  attempt to make it easy to turn the motor over during the timing chain and head gasket jobs, I wanted to put the crank bolt back in with some shims (to ensure it wasn’t bottoming out on the back of the crank threads), and when trying to thread this in through the damaged threads, I made matters worse.

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Fix and flip: The Saga of the 2000 S10, Part 9 (It’s Alive!)

First up, let’s get a timing chain on this thing.  I’ve pulled the old gears, chain, and tensioner.  The oil cup plug has a hole in it. This is where the oil sprays on the timing chin to lubricate it:

There is a tech service bulletin out on this.  The new ones have a slightly larger hole to supply more oil to the chain to prevent timing chain failure.  So we need to get the old cup out and install the new one.

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Fix and flip: The Saga of the 2000 S10, Part 5

S10 Update:

I couldn’t find my compression tester, and ran out to Harbor Freight to pick up a leak down tester so I can stop borrowing them from friends. This is just going to be easier than a compression tester with the state the motor is in.

Bottom line: I have at least 2 bad valves that won’t seal.  Bent or cruddy?  Don’t know.


For anyone interested in a leak down test on a motor with the exhaust manifold and throttle body already off, here it is: