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Eric,
I want to thank you for what your doing helping DIY wrench heads like me. My wife has a 2002 Chevy Trailblazer, the other day I started the car and made it about half way down my street and the car just shut off. After pushing it back up the street and into the driveway I started to Dx. the problem. I check all of the fuses and relays # 41 is for the fuel pump, I switched it out with the horn relay and it just turned over. I check for fuel pressure and it was zero, so I assumed it was the fuel pump (in the tank) after spending $300.00 for a new one, I put it back together (I tested it before I installed it and it was fine) when I tried starting it…… nothing. I then removed the new fuel pump and returned it for another one, same thing…nothing. I checked the voltage at the wire harness and turned the key on and it read zero volts. I checked a bunch of forums to see if I could find an answer….One of them said it could be the oil pressure sending unit, so I changed it….NOTHING. I hit a wall. Will a bad ECM cause this? The car has over 200,000 miles on it and we really haven’t had problems with it. The Transmission is starting to slip and I have a rebuilt one to install. What would you suggest next?
Thanks,
Newcastle Utd.
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One way is to verify all powers and grounds to your pcm and if you look at that wiring diagram it says that at terminal 3 of the c2 connector at the pcm should be your fuel pump relay control which according to the diagram looks like its supplying power so what you do is verify your powers and grounds in and if you do not have fuel pump relay control out then its pretty safe to say you have a bad pcm. Reason being is you have power and ground inputs but no output. Another way to verify this would be find out which leg of the terminal is fed by the pcm and apply power to that wire if your vehicle runs then theres a good possibility its the control
You don’t really ‘test’ a PCM, you eliminate all other possibilities and then try a known good PCM. That’s pretty much the ‘test’.
I would recommend you check for power going to that relay as suggested. There could be an issue with the relay or the wiring to it. Just because you don’t have power at the pump that doesn’t mean that the PCM is bad. There is a relay and some wiring to consider first. Personally I’d throw out the diagnosis you’re mechanic has done up to this point as he didn’t seem to come to a conclusion. Follow the voltage first and find out where it’s missing. If it’s not coming out of the computer then make sure the computer is getting an input signal from the ignition switch to activated. If it is and all the wiring and relay are good, THEN replace the PCM, not before.
OK here’s the update,
I traced the wire from the Relay # 41,it has 4 pins.
Pin# 1 Top L – gray wire to tank, good continuity.
Pin# 2 Top R -open to the ground (black), good continuity to Red (+)
Pin# 3 bottom L – goes to ground.
Pin# 4 Bottom R – 12.4 Volts.I jumped # 4 and #1 and the fuel pump started running.
I started the car but it runs rough. I pull the jumper and it dies. It was running perfect when it died so I don’t think it’s a head gasket .How many votes for PCM ? :woohoo:
? ? ? :sick:
It defiantly looks like you’ve nailed it down to a signal issue, well done. That said you still can’t say it’s the PCM. You need to make sure the PCM is getting it’s ignition signal TELLING it to turn on the fuel pump. I think the next step is to verify that the PCM is getting that signal. If it is then replace the PCM, if not then find out why.
I got a replacement PCM. Any ideas how to install it. I know I have a pass key 3. The guy who sold it to me said it takes a certain pattern before it will work. He didn’t have any information until Monday. He didn’t know how to use the scanner????
there are two balts on the back of the pcm you should have no problem with the secerty. if it works you need to have it re flashed to your vin,
When I bought it they already flashed it to my Vin and mileage. I thought I had to have the PCM relearn the key. Am I wrong?
I found this
PASSKEY 3 AND PASSKEY 3+In this system, the vehicle theft deterrent functions are provided by the theft deterrent control module. There is a transponder embedded in the head of the key that becomes energized by the exciter coils in the ignition lock cylinder when the ignition switch is turned on. The energized transponder now transmits a signal containing a unique value to the theft deterrent control module. If the module accepts this value, then there is an additional communication that takes place between the module and the key. If the module and the key agree, then the module sends the fuel enable password to the PCM. If the PCM recognizes the password, then the vehicle starts and runs normally. If any of the communication between the module and the key is incorrect or the PCM does not recognize the password, then the fuel injectors are disabled. The ignition key is a normal looking key with no visible contacts as in the Passkey or VATS systems. The transponder is located in the key head. The transponder value is fixed and cannot be changed. These keys are usually identified by the letters PK3, or PK3+ stamped into the steel body. A relearn will be necessary if any of the following have been replaced: any key, the theft deterrent control module or the powertrain control module (PCM). When the theft control module is being replaced, the module will learn the existing keys immediately. However, the PCM must learn the new fuel enable password from the new module. If you are replacing a PCM with a PCM that has been used in another vehicle or has been remanufactured, then a relearn must be performed in order for the PCM to learn the fuel enable password. Keep in mind that when you perform a relearn on this system, all previously learned keys will be erased from the theft deterrent control module’s memory. Any additional keys may be relearned immediately after the first relearn has been performed by inserting the additional key and turning the ignition switch to the “On” position within ten seconds of removing the previously learned key.
In order to initiate the relearn process:
1. Insert a master key (black head) into the ignition switch.
2. Turn to the “On” position without starting the engine. The security light should illuminate and stay on.
3. Wait approximately 10 minutes or until the security light turns off.
4. Turn off the ignition switch and wait 5 seconds.
5. Repeat steps 2 through 4 two more times with the same key.
6. Turn the ignition off. The vehicle will now learn the key transponder information on the next start cycle.
7. Start the vehicle. If vehicle starts and runs normally, and security light is off, the relearn is complete.
If additional keys are to be relearned:
8. Turn the vehicle off.
9. Insert the next key to be learned and turn the ignition switch to the “On” position within 10 seconds of removing the previously used key.
10. Wait for the security light to turn off. It should happen quickly. You may not even notice the light come on, because it will learn the key transponder immediately.
11. Repeat steps 8 through 10 for any additional keys.
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CRANKSHAFT VARIATION RELEARN (CASE Learn)
”CASE” means: crankshaft angle sensor error. A crankshaft variation relearn must be performed if:
A diagnostic trouble code of P1336 is present.
The computer has been replaced or re-programmed.
The crankshaft position sensor has been replaced.
The engine, harmonic balancer, clutch, or flywheel have been: disassembled, removed, or replaced.
The crankshaft position variation learning feature enables the computer to compensate for part manufacturing tolerances. This allows the computer to accurately detect an engine misfire throughout the engine RPM range. The learning process is stored in the computer’s memory and does not have to be repeated unless one or more of the above conditions are present.
To perform the relearn, proceed as follows:
Connect a scan tool to make sure there are no trouble codes stored in the computer’s memory. If there is any power train trouble code other than P1336 (Crankshaft Position Variation not learned), the computer will disable the relearn function until the problem that aused the code has been eliminated. Also, make sure that the engine coolant (check it when the engine is cold) and oil levels are at an acceptable level.
1. Set the parking brake and block the drive wheels. Make sure that the hood is closed.
2. Start the engine and make sure that the engine coolant temperature is at least 158 degrees F. (70 degrees C.)
3. Turn the engine off for at least 10 seconds.
4. Select the crankshaft position variation learn procedure (CASE Learn)on your scan tool.
5. Make sure that the transmission is in Park. Start the engine.
6. Apply the brakes and hold the pedal firmly.
7. Follow the scan tool instructions.
Remember: That you are going to increase the engine speed to approximately 3000 RPM, 4000 RPM, or 5150 RPM. That’s the variation learn fuel cutoff RPM (depending upon the engine), and that it’s important to release the throttle when the engine RPM starts to decrease as a result of the fuel cutoff going into effect. Failure to do such will result in over revving of the engine, causing possible engine damage.
8. Once the engine has returned to idle, check the status of Diagnostic trouble code P1336. If the scan tool indicates that the CASE has been learned, the relearn procedure is now complete. If CASE has not been learned, check for the presence of other power train codes. If any exist, correct the problem, then repeat this procedure.
NOTE: If the Crankshaft Variation Relearn is not accessible through your scan tool (some truck applications 1998 & later), perform the relearn in the following manner:
1. Turn off all of the accessories. With the Air temperature sensor and Coolant temperature within 5 degrees (Centigrade) of each other, start the engine and let it idle in Park or Neutral for two minutes.
2. Accelerate the vehicle to 55 mph at part throttle. Cruise at 55 mph for 8- 10 minutes until the engine reaches operating temperature.
3. Cruise at 55 mph for another 5-6 minutes.
4. Decelerate to 45 mph without using the brakes, and maintain 45 mph for 1 minute.
5. Perform 4 deceleration cycles, without using the brakes, of 25 seconds each where no specific speed is necessary. Returning to 45 mph for 15 seconds in between deceleration cycles.
6. Accelerate to 55 mph and cruise for 2 minutes.
7. Stop the vehicle and idle for 2 minutes with the brake applied and the transmission in Drive (automatic trans.) or Neutral (manual trans.) with the clutch depressed. Refer to diagram A on page 8.
BASE IDLE RELEARN
The Computer will reset the idle air control valve whenever the ignition switch is turned to the “On” position, then to the “Off” position. However, before you return the car to the customer, it is best to bring the engine up to operating temperature in Park with the air conditioning off. Then, turn the air conditioning on. Next, turn the air conditioning off. Next, place the transmission selector in drive. Finally, with the car in Drive, turn the air conditioning on. That’s it!
DIESEL ENGINE TDC OFFSET RELEARN PROCEDURES
This procedure should only be performed when one or more of the following has occurred:
1. A diagnostic trouble code of P1214 (TDC offset not established) is present.
2. The engine has been replaced.
3. The front engine cover has been replaced.
4. The PCM with or without the injection pump has been replaced.
5. The crankshaft position sensor has been replaced.
NOTE: Replacement of the only the injection pump does not require this procedure.
In order to initiate the relearn:
1. Hook up your scan tool.
2. Start the engine and idle engine until coolant temperature is at least 170 degrees F.
3. Clear any diagnostic trouble codes, if any. Then turn the engine off.
4. Turn the ignition switch to the “On” position. Do not start the engine.
5. Prepare the PCM to activate the offset relearn by placing and holding the accelerator pedal in the fully open position for no less than 45 seconds. Then release the pedal.
6. Turn the ignition switch to the “Off” position for 30 seconds. To confirm that the PCM has powered down, you should get a “No communication with vehicle” message on your scan tool.
7. Now start the engine and make sure that the coolant temperature is 170 degrees F or higher.
8. As soon as the engine coolant has reached 170 degrees F. and the engine speed is below 1500 RPM, the PCM will automatically learn the new TDC offset. A slight stumble in engine RPM is indicative that the new TDC has been activated.
9. Verify the TDC offset reading on your scan tool. The TDC offset should be between -0.25 and –0.75 degrees. If the TDC offset is within the specification, the relearn is completed. If the offset is out of specification then the injection pump must be adjusted. If the injection pump has not been replaced or adjusted and the TDC offset is very high on the positive side, then check for damage on the camshaft driven gear or key-way. If the TDC offset is very high on the negative side, check the crankshaft sensor for proper installation.
TRANSMISSION RELEARN
There is no relearn procedure other than to drive the vehicle. It is best to road test the vehicle, as the PCM will relearn the adaptive pressure shift points for proper transmission operation. The transmission may not shift as usual until the shift points have been learned. It is recommended that the first shift sequence be performed manually. Shift the transmission from low (first) gear to overdrive, one gear at a time, under moderate acceleration. If you turn the vehicle over to the customer without a road test, you may want to call this to their attention.
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