Electronic Engine Controls and Sensors | Testing Procedures

All Sequential Fuel Injection (SFI) systems use the EEC system. The heart of the EEC system is a microprocessor called the Powertrain Control Module (PCM). The PCM receives data from a number of sensors and other electronic components (switches, relays, etc.). Based on information received and information programmed in the PCM's memory, it generates output signals to control various relays, solenoids and other actuators. The PCM in the EEC system has calibration modules located inside the assembly that contain calibration specifications for optimizing emissions, fuel economy and driveability. The calibration module is called a PROM. Electronic Engine Controls and Sensor Testing Procedures Powertrain Control Module (PCM) Throttle Position (TP) sensor Mass Air Flow (MAF) sensor Intake Air Temperature (IAT) sensor Idle Air Control (IAC) valve Engine Coolant Temperature (ECT) sensor Heated Oxygen Sensor (HO2S) Camshaft Position (CMP) sensor Knock Sensor (KS) Vehicle Speed Sensor (VSS) Crankshaft Position (CKP) sensor

WHAT COULD CAUSE THE ENGINE TO STALL WHILE DRIVING - 2002 Toyota Prius

Recall ID # 06V266000 - ENGINE AND ENGINE COOLING - Recall Date:JUL 19, 2006 Model Affected:2002 TOYOTA PRIUS Summary:ON CERTAIN PASSENGER VEHICLES, DUE TO IMPROPER MOLDING OF THE RESIN BODY OF THE CRANKSHAFT POSITION SENOR INSTALLED ON THE ENGINE BLOCK, ENGINE OIL MAY PENETRATE THE SEAL AND ENTER THE SENSOR WIRING CONNECTOR. THE WIRE HARNESS CONNECTOR MAY NOT BE SUFFICIENTLY ATTACHED TO THE LOCKING TAB OF THE SENSOR WIRING CONNECTOR. Consequence:ENGINE OIL INSIDE THE SENSOR WIRING CONNECTOR COULD CAUSE EXPANSION DUE TO THE HEAT OF THE ENGINE AND COULD DEFORM THE SENSOR WIRING CONNECTOR. THE CONNECTOR MAY BECOME DISCONNECTED, WHICH COULD CAUSE THE ENGINE TO STALL WHILE DRIVING AND NOT BE ABLE TO BE RESTARTED INCREASING THE RISK OF A CRASH. Remedy:DEALERS WILL REPLACE THE CRANKSHAFT POSITION SENSOR FREE OF CHARGE. THE RECALL BEGAN ON JULY 26, 2006. OWNERS MAY CONTACT TOYOTA AT 1-800-331-4331. Potential Units Affected:34771 Notes:TOYOTA MOTOR NORTH AMERICA, INC. 60G

Air Conditioning pressure cycling switch

Question:

I have a 1994 Chevy truck and I need to recharge the air conditioning. When i hook up the can of R134a Freon the compressor does not engage to suck in the freon. Could it be a bad Air Conditioning Pressure Cycling Switch?

Answer:

The situation you are running into is normal. The compressor will not engage until there is enough pressure seen at the air conditioning low pressure cycling switch. So what you will need to do is manually bypass the switch with a jumper wire. This will engage the compressor and allow it to suck in the freon. After you have installed one can (14 oz.), then remove the jumper wire and finish the recharge cycle with the pressure cycling switch plugged in.

How to Recharge Air Conditioning

Chevy Code 42

Had a customer bring in a 1989 Chevy Van G20, 5.7L with a stumble issue and intermittent stall. The check engine light was on .The check engine light codes can be Extracted without a scan tool. The code that was extracted was Code 42 : Electronic spark timing (EST) circuit fault. A quick read of a great article on Code 42 that covers the specific components involved : The EST system consists of the ignition module, computer (ECM/PCM), and the connecting wiring. Used a Multi-meter to test and check the wiring and found no issues, but what was noticed is the fuel injectors would click several times by themselves with the key off. This was a bit strange, but lead me to believe there had to be a short somewhere causing this and sure enough there was an internal short in the ECM. Purchased an ECM for the local parts house for just under $100.00 and replaced it. The engine no longer has the stumble and it no longer puffs smoke when you start it up (originally thought to be valve seals gone bad). Customer happy! Side note* I did try a new EST first as it was easy to get to and a quick test. It is located under the drivers seat along with the ECM.

Check Engine Light On, What Do I do ?

When the Check Engine Light comes on and keeps a steady light the computer is letting you know there is an issue with one of the sensors or sensor readings. When the Check Engine Light is flashing the computer is letting you know that something serious is wrong and the vehicle should not be driven more than a mile and then towed to prevent irreversible damage.

On vehicles that are 1996 and newer, It requires the use of a Scan Tool to extract the check engine light codes. Once you have the code you can look out the code definition and determine the best course of action for the issue. Once the repairs are completed you will need to clear the codes out of the computers memory with the Scan Tool.

Gas Mileage Lower than Normal?

Today’s engine management systems rely on many different sensor inputs to regulate fuel economy, performance and emissions.

Symptom: Poor Fuel Economy

Probable Causes: Fuel Rich Codes (P0172 and/or P0175)

With the price of gasoline, you don’t want to ignore this kind of problem for long. When fuel economy is down, you may find any number of codes: • P0172 and/or P0175 are rich codes, and indicate a general rich air/fuel condition. The underlying cause may be anything that increases fuel delivery, such as excessive fuel pressure, a defective fuel pressure regulator, plugged return line, or leaky injectors. Decreased airflow from a dirty air filter or restricted air intake misleads the mass airflow sensor or engine management system into believing the engine is using more air or is under more load than actual.

Code P0720, P0731, P1790,P0700

Customer Problem:

I have a 1999 Chrysler 300M with a 3.5L engine. My Check Engine light came on and at the same time I lost my dash gauges and it will not shift out of first gear.

Solution:

Computer Diagnostics done to extract the codes for the check engine light. The coeds were:

P0720 = Output shaft speed sensor error

P0731 = First gear incorrect ratio

P1790 = Fault immediately after shift

P0700 = Transmission fault code

Since this situation all happened at once it would make sense that they are related. After removing and testing the Output shaft sensor that is supposed to be at 800 ohms, and was showing completely open, the Output shaft sensor was proven to have failed. Replaced the Output Shaft Sensor ( $20.00 ) and cleared the codes. Test drove the vehicle and all is working normal. Customer happy.

Tire Pressure Sensor

If your tire pressure sensor keeps coming on and that anoying light on the dash just keeps staring at you while your driving, then maybe its time to correct the problem.

tire pressure monitoring system (TPMS) is an electronic system to monitor the air pressure inside a pneumatic tire. They are sometimes referred to as remote tire pressure monitoring systems (RTPMS) or simply as run flat indicators.

Direct Direct TPMS delivers real time tire pressure information to the driver of the vehicle - either via a gauge or a simple low pressure warning light. These systems employ physical pressure sensors inside each tire and a means of sending that information from inside the tire to the vehicle instrument cluster. Indirect Indirect TPMS measures the air pressure indirectly by monitoring individual wheel speeds and other signals available in the vehicle. Most indirect TPMS uses the fact that an under-inflated tire has a slightly smaller diameter than a correctly inflated tire and therefore has to rotate more times to cover a specific distance to detect under-inflation. Such TPMS can detect under-inflation in up to three tires simultaneously but not in all four since the operating principle of these systems is to compare the different wheel speeds and if all four tires lose the same amount of air the relative change will be zero. Newer developments of indirect TPMS can also detect simultaneous under-inflation in all four tires thanks to vibration analysis of individual wheels or analysis of load shift effects during acceleration and/or cornering. Indirect TPMS is cheap and easy to implement since most modern vehicles already have wheel speed sensors for anti-lock braking systems and electronic stability control systems. The disadvantage is that they rely on the user resetting the system by pushing a "Calibration Button" when the tires are changed or re-inflated—forgetting to perform this initialization leads to potentially dangerous false or missing alerts. Another disadvantage of indirect TPMS is that if the Calibration Reset Button is pressed when one or more tires are under-inflated then the system accepts this under-inflation as normal and the driver will be unaware of potentially dangerous tire pressures.

This means you will need to make certain you have no leak and you keep your tire pressure on all tires within 3 psi. No keep in mind if your front tires tread is worn more than the rear, then it will effect the reading as well. So lets keep the tire pressure topped off often.

If for some reason you would need to replace a set of sensors, they run about $200.00 for a set from your local dealer.

Reference : http://en.wikipedia.org/wiki/Tire_Pressure_Monitoring_System

What is an IAC ?

Idle Air Control (IAC) Valve

OPERATION

The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows the necessary amount of air, as determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.

TESTING

Turn the ignition switch to the OFF position. Disengage the wiring harness connector from the IAC valve . Using an ohmmeter, measure the resistance between the terminals of the valve. NOTE: Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR terminal and the negative lead on the ISC terminal. If the resistance is not 7–13 ohms, replace the IAC valve.

Oxygen Sensors

OXYGEN (O2) SENSORS

General Information An Oxygen (O2) sensor is an input device used by the engine control computer to monitor the amount of oxygen in the exhaust gas stream. This information is used by the computer, along with other inputs, to fine-tune the air/fuel mixture so that the engine can run with the greatest efficiency in all conditions. The O2sensor sends this information to the computer in the form of a 100–900 millivolt (mV) reference signal, which is actually created by the O2sensor itself through chemical interactions between the sensor tip material (zirconium dioxide in almost all cases), the oxygen levels in the exhaust gas stream, and ambient atmosphere gas. At operating temperatures, approximately 1100°F (600°C), the element becomes a semiconductor. Essentially, through the differing levels of oxygen in the exhaust gas stream and in the surrounding atmosphere, the sensor creates a voltage signal which is directly and consistently related to the concentration of oxygen in the exhaust stream. Typically, a higher than normal amount of oxygen in the exhaust stream indicates that not all of the available oxygen was used in the combustion process, because there was not enough fuel (lean condition) present. Inversely, a lower than normal concentration of oxygen in the exhaust stream indicates that a large amount was used in the combustion process, because a larger than necessary amount of fuel was present (rich condition). Thus, the engine control computer can correct the amount of fuel introduced into the combustion chambers.

Since the control computer uses the O2sensor output voltage as an indication of the oxygen concentration, and the oxygen concentration directly affects O2sensor output, the signal voltage from the sensor to the computer fluctuates constantly. This fluctuation is caused by the nature of the interaction between the computer and the O2sensor, which follows a general pattern: detect, compare, compensate, detect, compare, compensate, etc. This means that when the computer detects a lean signal from the O2sensor, it compares the reading with known parameters stored within its memory. It calculates that there is too much oxygen present in the exhaust gases, so it compensates by adding more fuel to the air/fuel mixture. This, in turn, causes the O2sensor to send a rich signal to the computer, which then compares this new signal, and adjusts the air/fuel mixture again. This pattern constantly repeats itself: detect rich, compare, compensate lean, detect lean, compare, compensate rich, etc. Since the O2sensor fluctuates between rich and lean, and because the lean limit for sensor output is 100 mV and the rich limit is 900 mV, the proper voltage signal from a normally functioning O2sensor consistently fluctuates between 100–300 and 700–900 mV.

NOTE: The sensor voltage may never quite reach 100 or 900 mV, but it should fluctuate from at least below 300 mV to above 700 mV, and the mid-point of the fluctuations should be centered around 500 mV.

To improve O2sensor efficiency, newer O2sensors were designed with a built-in heating element, and were called Heated Oxygen (HO2) sensors. This heating element was incorporated into the sensor so that the sensor would reach optimal operating temperature quicker, meaning that the O2sensor output signal could be used by the engine control computer sooner. Because the sensor reaches optimal temperature quicker, modern vehicles enjoy improved driveability and fuel economy even before the engine reaches normal operating temperature.

On-Board Diagnostics second generation (OBD-II), an updated system based on the former OBD-I, calls for additional O2sensors to be used after the catalytic converter, so that catalytic converter efficiency can be measured by the vehicle's engine control computer. The O2sensors mounted in the exhaust system after the catalytic converters are not used to affect air/fuel mixture; they are used solely to monitor catalytic converter efficiency.