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Ask Chad Farhat Your Own Question
Chad Farhat
Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems
Category: Chevy
Satisfied Customers: 2037
Experience:  Owner at Carolina Auto Service & Sales , 20 years Experience in Foreign & Domestic vehicles A6 - Electrical / Electronic systems A7 Heating / Air Conditioning systems
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I have a 2000 chevy blazer with po300 and po171, yes cleared

Customer Question

I have a 2000 chevy blazer with po300 and po171
JA: Are you fixing your Blazer yourself? What have you tried so far?
Customer: yes I am I cleared codes checked all vaccum hoses and drove it the light came on in about 15 mins but ran perfect with light off
JA: Just to clarify, what are the exact lights you're talking about?
Customer: service engine light
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 2 months ago.
Category: Chevy
Expert:  Chad Farhat replied 2 months ago.

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

Customer: replied 2 months ago.
I have a 2000 Chevy blazer with po300 an po171 codes
Customer: replied 2 months ago.
U there
Expert:  Chad Farhat replied 2 months ago.

1- have you cleaned the Mass air flow sensor

2- do you have a scanner that reads fuel trims ?

3- the P0171 is

CIRCUIT DESCRIPTION In order to provide the best possible combination of driveability, fuel economy, and emission control, the vehicle uses a Closed Loop air and fuel metering system. While in closed loop, the VCM monitors the oxygen sensor signal voltage. The Vehicle Control Module (VCM) adjusts the fuel delivery based on the signal voltage. The Long and Short Term fuel values, which a scan tool can monitor, indicate a change made to the fuel delivery. Ideal Fuel Trim values are around 0 percent (128 counts). If the oxygen sensor signal indicates a lean condition, the VCM adds fuel. This results in fuel trim values above 0 percent. If the oxygen sensor detects a rich condition, the Fuel Trim values will read below 0 percent. This indicates that the VCM is reducing the amount of fuel delivered. The VCM sets this DTC when an excessively lean condition is detected.

3- TSB P0330

There is A TSB I want to read make sure it is not the problem here

Bulletin No.: 02-06-05-004b Date: February 14, 2006 INFORMATION Subject: Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems Models: 2006 and Prior GM Passenger Cars and Light Duty Trucks 2006 and Prior HUMMER H2, H3 2006 and Prior Isuzu Light Duty Trucks Supercede: This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 02-06-05-004A (Section 06 - Engine/Propulsion System). General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles. These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Overtime, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly. Important: Engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. Because of this, it has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition. Dealers must be aware of this issue and take note of the wiring on vehicles with alarm systems that come in for repair, particularly for catalytic converter damage that seem to have no known root cause.

P0300

CIRCUIT DESCRIPTION The Crankshaft Position (CKP) sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the control module will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or in all cylinders randomly. When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The control module determines which cylinder has misfired based upon the Camshaft Position (CMP) sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, this Diagnostic Trouble Code (DTC) will set. CONDITIONS FOR RUNNING THE DTC IMPORTANT: If start-up ECT is below -7°C (20°F), misfire detection is delayed until ECT is more than 21°C (70°F). If start-up ECT is more than -7°C (20°F), misfire detection begins after a 5 second delay. ^ No active VS sensor DTCs ^ No active TP sensor DTCs ^ No active MAF sensor DTCs ^ No active CKP sensor DTCs ^ No active CMP sensor DTCs ^ The fuel level is more than 10 percent. ^ The engine speed is between 450-5000 RPM. ^ The system voltage is between 11-16 volts. ^ The throttle position is steady within 2 percent for 100 ms. CONDITIONS FOR SETTING THE DTC The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire. ACTION TAKEN WHEN THE DTC SETS If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the Malfunction Indicator Lamp (MIL) after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present. CONDITIONS FOR CLEARING THE MIL OR DTC ^ The control module turns OFF the MIL after*****trips when the test has run and passed. ^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. ^ Use a scan tool in order to clear the DTCs. DIAGNOSTIC AIDS The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present. Many different condition could cause an intermittent misfire. Check for the following conditions: ^ Check the IC control circuit for a intermittent short to ground. ^ Check the spark plug wires and the coil wire for the following conditions: - Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap. - Check the wire routing in order to ensure that cross-firing is not occurring. - If the misfire occurs when the weather is damp, the problem could be due to worn plug wires. ^ Check for contaminated fuel or a low fuel level and the following conditions: - Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition. - If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and possible misfire condition. Check the fuel trim numbers in the Freeze Frame to determine if this has occurred. It would be likely if the short term fuel number was above + 20. ^ Check HO2S for abnormal voltage readings. ^ Check for a vacuum leak as a possible cause of the engine misfire. ^ Sticking intake or exhaust valves can cause a misfire when the Engine is cold. An intermittent may be caused by any of the following conditions: ^ A poor connection ^ Rubbed through wire insulation ^ A broken wire inside the insulation

TEST DESCRIPTION The numbers below refer to the step numbers on the diagnostic table. 5. The misfire is considered random on all cylinders if, while viewing the misfire counters in the misfire data list, the misfire seems to move to different cylinders. 6. The misfire is considered consistent if the misfire is occurring on the same cylinders consistently. 7. When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.

Let me know if you need anything else on it , just reply back here & we can continue.

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Chad Farhat
ASE Certified Tedchnician

Expert:  Chad Farhat replied 2 months ago.

you need to address P0171 first , it could be causing the P0300,

most likely the Oxygen sensor , what is the mileage on it ?

Customer: replied 2 months ago.
224000
Customer: replied 2 months ago.
I haven't cleaned mass air yet the truck has been sitting sereveral months
Expert:  Chad Farhat replied 2 months ago.

you need to address P0171 first , it could be causing the P0300,

most likely the Oxygen sensor , what is the mileage on it ?

Clean Mass air flow sensor and Retest if it has been sitting ,if it comes back

look into the Oxygen sensor Bank 1 Sensor 1

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Customer: replied 2 months ago.
I just get mass air flow cleaner an spray it down
Expert:  Chad Farhat replied 2 months ago.

yes you can buy from local parts store

when you spray it make sure you leave it outside in the sun to dry before installation and do not tough the little metal strip on inside by hand .

Chad

Customer: replied 2 months ago.
Ok
Expert:  Chad Farhat replied 2 months ago.

in case check engine light came back , get me some fuel trims reading and post them back here and we can go further on it if need be.

I m online daily from 10 am til late

Chad

Expert:  Chad Farhat replied 2 months ago.

Please let me know if you need anything else on it, just reply back and we will continue

If you are good, Please Kindly Rate Me.

A 5 Star Rating is much Appreciated

If you feel I have not been helpful Please DO NOT RATE ME BAD OR POOR (1 or 2 stars) ,You can always ask me again or I can opt out of your question & open it for another expert ,that will provide you with more or better assistance on this issue

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you can always come back to this conversation and ask me any follow up question you may have on this issue

(you can copy this link page & paste it in your browser when ready and it will open up our conversation again)

Thank You
Chad Farhat
ASE Certified Technician

Expert:  Chad Farhat replied 2 months ago.

Please let me know if you need anything else on it, just reply back and we will continue

If you are good, Please Kindly Rate Me.

A 5 Star Rating is much Appreciated

If you feel I have not been helpful Please DO NOT RATE ME BAD OR POOR (1 or 2 stars) ,You can always ask me again or I can opt out of your question & open it for another expert ,that will provide you with more or better assistance on this issue

Please keep in mind that when you rate me , it does not end our conversation.

you can always come back to this conversation and ask me any follow up question you may have on this issue

(you can copy this link page & paste it in your browser when ready and it will open up our conversation again)

Thank You
Chad Farhat
ASE Certified Technician