CBCJH COMPUTERS AND INPUT SENSORS CHAPTER 8

CBCJH VOLTAGE SIGNALS l ANALOG VOLTAGE SIGNALS –VARIABLE VOLTAGE SIGNAL –COMPUTERS INPUTS ARE USUALLY ANALOG TYPE SIGNALS –EASY TO DIAGNOSE WITH DVOM –DIRECT CURRENT OR ALTERNATING CURRENT Pg 153C

CBCJH DIGITAL VOLTAGE SIGNALS l VOLTAGE IS EITHER HIGH OR LOW IN A GIVEN TIME PERIOD l COMPUTER USES AND PROCESSES INFORMATION IN DIGITAL LANGUAGE (BINARY 0 or 1) l SOME INPUTS PRODUCE A SQUARE WAVE SIGNAL Pg 154C

CBCJH COMPUTER OPERATION l INPUT CONDITIONING –AMPLIFICATION –ANALOG TO DIGITAL CONVERSION –SOME A/D CONVERTER EXTERNAL TO MAIN PROCESSOR. (LIKE FORD PROGRAMMABLE SPEED ONLY MEMORY - PSOM) Pg 155C

CBCJH COMPUTER MEMORY l RAM - RANDOM ACCESS MEMORY –TEMPORARY STORAGE – VOLATILE OR NON-VOLATILE l ROM - READ ONLY MEMORY l PROM - PROGRAMMABLE READ ONLY MEMORY –TELLS MICROPROCESSOR HOW VEHICLE IS EQUIPPED Pg 159C

CBCJH COMPUTER PROGRAMMED STRATEGY l OPEN LOOP - CLOSED LOOP l ADAPTIVE STRATEGY –ABILITY OF COMPUTER TO LEARN FROM PAST EXPERIENCE. –COMPENSATES FOR WEAR u Will lose learned strategy if: –BATTERY DISCONNECTED –WHEN MAJOR COMPONENT REPLACED –NEW VEHICLE Pg 160C

CBCJH INPUT PROCESSING l ROM LOOK UP TABLES (Pg 162C) l COMPUTER TAKES ALL INPUT INFO BEFORE MAKING DECISION l ONE WIRE INPUT (Pg 140L & 154L) l TWO WIRE INPUT (Pg 142L & 143L) l THREE WIRE INPUT (Pg 144L) l FOUR WIRE INPUT (Pg 146L)

CBCJH PINPOINT TESTING l MOST REPAIR MANUALS TELL TO CAUSE OPPOSITE CODE l OHMMETER VS. VOLTMETER l FREQUENCY INPUT TESTING l LAB SCOPE USE l BLOCK LEARN - INTEGRATOR

CBCJH OXYGEN SENSORS l 1,2,3,4 Wire s l EGO, HEGO l Lean Low Volts l Rich High Volts l Zirconia Type l Titania Type l DVOM or Lab Scope Only!!! PAGE 168C

CBCJH ECT/ACT SENSORS l THERMISTORS HIGH RESISTANCE COLD AND LOWER RESISTANCE HOT PG 142L

CBCJH THROTTLE POSITION SENSORS (TPS) l ROTARY AND LINEAR l MUST BE SMOOTH VOLTAGE CHANGE l BEST TO USE A LAB SCOPE FOR TEST PG 145L

CBCJH THROTTLE SWITCH l Four Wire Sensor l Used on alot of Foreign Cars and Trucks l Adjustment is critical l Some switches used as Fuel Pump Shut Off Pg 146L

CBCJH MANIFOLD ABSOLUTE PRESSURE SENSOR l Senses differences between atmospheric pressure and manifold vacuum. l Must use specialized equipment to test l Sometimes used for BARO Input information Pg 147L

CBCJH MASS AIR FLOW SENSORS l VANE TYPE l Commonly used on foreign Cars l Test with DVOM or Lab Scope l Plate movement proportional to Air Flow l Other Inputs l HOT WIRE TYPE or GRID TYPE l Use Frequency Test l Map Frequency should always be a straight line transition with rpm. l Tap Test Pg 151L Pg 152L

CBCJH KNOCK SENSORS l PIEZOELECTRIC CRYSTAL l Produces a frequency and changes it to a voltage before sending to PCM l TAP TEST, DVOM, FREQ or OHMMETER

CBCJH EGR SENSORS l EVP Linear Sensor l Must test mechanical and electrical l Many different types of EGR & ``EGR Controls and EGR Sensors l Most EVP’s send a Analog signal l Lots of Driveability Problems l EGR problems can be caused by other Inputs Pg 154L Pg 317L

CBCJH VEHICLE SPEED SENSORS l AC SIGNAL (ANALOG) l LOCATED DIFFERENT PLACES l SPEED BUFFER OR PSOM l CAN CAUSE TCC, CRUISE, SPEEDOMETER PROBLEMS

CBCJH NEUTRAL DRIVE SWITCH

CBCJH OUTPUTS l ACTUATORS –SOLENOIDS –RELAYS –DISPLAYS l CONTROLLED BY DRIVERS l TRANSISTORS OR GROUPS OF TRANSISTORS

CBCJH STUDY HARD AND ABSORB!!