I've been wanting to get a thread posted that will help members identify what is going on when their truck sets a DTC (data trouble code) or SES light.
If your truck sets a DTC, the first thing to do is, get it read. Don't guess and assume, get it read so you know if it's critical or not. IF the truck's drivability is good, then chances are you're not going to damage anything driving to the auto store to get the DTC read.
Most auto parts stores will read the code and attempt to decipher the code at no charge, so take advantage of it.
There are far too many codes to list every possible cause, so I'm going to keep this post to the most common DTC's.
Also, keep in mind there are going to be text book reasons for each code and how to troubleshoot them. There are also reasons why these codes set when a truck is modified a certain way, that no text book or troubleshooting tree is going to fix. These are types of codes that appear because the parameters in the calibration have to be changed, due to a certain mechanical change.
So, please don't reply with a book of reasons and steps on how to fix a DTC that was copied and pasted from AllData, lol. Most of us have modified our trucks to a point that our grew the stock pcm parameters.
I'd like to keep this post simple, for example, a dtc is set, here's the fix.
I'll start with a few and if it doesn't catch on, no biggy.
P0068 - MAP/MAF Throttle Position Correlation
- Had a customer come in one day, said his PCM was bad because this code kept coming up after clearing it. I thought it was feasible, so we swapped in a new PCM. Started the truck up and right away this code appeared. In the end, it turned out to be the TAC, Throttle Actuator Controller.
P0101 - MAF Performance
- You may have added too many bolt-on's and exceeded the maf's table that limits airflow. The truck may shutdown under wot as well.
P0171 - Fuel Trim System Lean Bank 1
- The ltrims have reached thier limit on adding fuel. There is a possible vacuum leak between the maf and o2 sensor. Locate a smoke machine and find the leak.
- Check fuel pressure. If there isn't enough fuel pressure at idle, then the pcm has to increase fuel to maintain stoich. The pcm can only add so much before this code is set.
- Something is up with the o2 sensor. Be sure it's reading correctly. It should be toggling from 20mv to 900mv.
P0300 - Engine Misfire Detected
- Did you just install a cam and not get a retune! That's why.
- There are many things that will also cause this, ignition, injector, coils, plugs, plugwire, harness. This one can get lengthy.
P0315 - Crankshaft Position System Variation not Learned
- Happens when a new pcm is installed
- If you removed the crank sensor or did an engine swap, this code will appear.
- Somtimes it just shows up, find a good shop with a quality scanner and ask them to perform a Crankshaft Relearn. IF they don't what that is, go to the next shop.
P0420/430 - Catalyst System Low Efficiency
- The rear o2's have detected the cats aren't doing their job. Possibly because hi flow cats were installed. This has come up before when Dynatech LT's are installed. The cats are too hi flow'n and the rear o2's think the cats are gone or bad.
- The truck just has too many miles and it's time to gut or replace the cats. We've seen cats go out as quick as 2,000 miles and late as 200,000 miles.
P0455 - Evaporative Emission [EVAP] System Leak Detected
- Custom came in today and said this code has been coming up. He checked and replaced many parts only to find out the code still comes back. The message center also reports "Tighten Fuel Cap".
After every option was exhausted, we finally just turned the code off.
P0327 / P0332 - Knock Sensor
- If you haven't been pulling your engine or messing with the wiring, what typically happens is; water/moisture gets under the intake manifold and corrodes the connection or destroys the sensors.
Probably the best method is to replace the knock sensors. If that doesn't work.
The 99/00 PCM's, in trucks, have issues with false knock. The solution, without modifing the knock sensor tables and deleting the codes is to, upgrade to a 2002 PCM. The 02 PCM cures all the issues
with Knock Sensors.
Ok, this was just a test. Will this kind of thread help you guys troubleshoot your trucks if you run into a DTC?
I think if we all post our experiences and what each of you did to fix the DTC, then we might have a good database.
If not, say so, I'll delete post lol. This got me started because we get a lot of phone calls about DTC's. Most of the time, it's the same thing, so why not just point the caller to this link.
later,
allen
updated: 02-11-09
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Originally Posted by GasGuzzler
