Technician

Technician

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Techpaddle

Waddington, NY

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Question Answered: 

replace the fuel filter. If this doesn't cure it, then the fuel pump is going out. With less than a 1/4 tank, the weight of the fuel isn't enough to keep the pump running at the proper pressure. Have the fuel system pressure checked.


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491 and 492 indicates a possible intake leak which would cause the engine to run too lean, reducing the ability to accelerate and makes it stall on deceleration. Have the AIR system checked and the intake inspected.


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It takes 2 complete drive cycles to have the ECM to test all components and be in the ready mode. Since you didn't pass 5 times, I highly suspect an electrical problem with the ECM/PCM. Somehow, it does not have constant power for its memory therefore, the memory and status clears every time you shut the key off. This would also explain the odd cold idle situation, since the computer would run the engine on the default settings until it can recalibrate, usually 5 to 10 minutes. The first thing to check is all the fuses. Pull them out one at a time and check them with an ohmmeter, clean the blades and reinstall. Do this to both fuse boxes, under hood and rear. In the rear box, fuse 28 marked "spare" is not a spare fuse, it supplies power to the PCM,ECM and TCM. If this fails, it is an electrical issue between the fuse box and ECM. At the ECM connector, remove connector #1 and check for power on pin #20. It is red with a white stripe. If there is no power, splice in a wire with a fuse from the fuse box. If you're not comfortable doing this, return to the test shop and explain the situation of the ECM resetting and if they could do the test with the engine running. If they agree, drive the car for at least an hour and a half (city and highway) and bring it in without shutting it off.


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The tail/turn on this car uses a dual filament bulb (1157) so ground issues are not the problem. With a test light and the 4 way hazards on, carefully check for power at each of the terminal contacts at the bottom of the socket. If there is power, change the socket, if not, there is a broken wire somewhere between the steering column and bulb. The first thing to check is if the car has had trailer wiring installed. Trace back the trailer wires to where they are spliced into the car's wiring. The blue crimp connectors tend to rot wires. If not, it will take a little time to trace the problem through the electrical system.


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Question Answered: 

The ECM uses the sensor output for the speedometer, but also for the transmission and mixture controls. If it was a sensor, the trans would shift into O/D at 20 mph. It sounds more like the decoder chip or the circuit board at the back of the cluster that changes the pulse signals to a voltage signal that runs the speedo. Plug in a code reader that has live data capability and take it for a drive. Verify that the live data reads the proper mph's compared to the dash. If they are different, it's the C/B or decoder.


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It sounds like the blower motor resistor has gone defective. This controls the various speeds as selected by the switch.


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It's Mercedes way of saying " start saving your nickels." The wrench indicates service is due and the numbers tell you in how many miles the service is due in. The numbers start at 1500 and go into the negatives, if past due. Basically, you are due for an oil change in 147 miles/kilometers


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Question Answered: 

P1794 Powertrain Control Module Battery Direct Power Circuit. Basically, the PCM is not passing power properly, Check all fuses, especially dome light, as it powers a circuit to the PCM. Pull them and check not only for continuity, but for corrosion on the blades and clean/replace as necessary. The next is to clean the battery connections and ground connections from the battery to the engine and body. These are the most common issues. If the problem persists, have the alternator output checked.


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Question Answered: 

The serv TPM means "Service Tire Pressure Monitor system" The first thing that will need to be done is to have the module relearn the TPM wheel sensors. The vehicle may be confused as to the correct location of each tire pressure sensor. Whenever the tires are rotated this procedure has to be performed. If that procedure was performed then this could possibly be a faulty TPM sensor but will need to be scanned to confirm the problem.


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If the "smoke" you see is usually worse on defrost and has a sweet smell to it , leaving behind a fine film that has to be cleaned off, it is your heater core that is leaking, spraying a fine mist of antifreeze in the air. Check the center floor area around the console for signs of moisture or have the cooling system pressure checked.


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