TP Sensor Scaling GMC Suburban I

TP Sensor Scaling

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (less than 1.25 volts) to greater than 4.5 volts when throttle is held at WOT position.

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about .5 volt or at idle to about 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and for most other VCM control outputs. On non-adjustable TPS sensors, each time voltage drops below 1.25 volts and stops, VCM assumes this value as 0 throttle angle and measures percent throttle from this point on.

With Code P0123 set, throttle position will default to 19 percent and Tech 1 will not indicate fault value. VCM will illuminate Malfunction Indicator Light (MIL).

Note. Test numbers refer to numbers on diagnostic chart.

1. If TP signal is greater than 4.8 volts, fault is present.
2. With TP sensor disconnected, TP sensor voltage should decrease. This test verifies that VCM and wiring are okay.
3. Probing ground circuit with a test light checks sensor ground circuit. This isolates a faulty sensor, VCM or open ground circuit.

Code P0123, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 307

Tech 1 displays throttle position in volts. With closed throttle, ignition on, or at idle, voltage should be .45-.85 volt. If voltage is not as specified, replace TP sensor. Check for

Inspect VCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Monitor TP sensor voltage display on Tech 1 while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (less than 1.25 volts) to greater than 4.5 volts when throttle is held at WOT position.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks VSS circuit.
2. Checks integrity of sensor.
3. Checks 5-volt and ground circuits to VCM.

Code P0502/503, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 308

Code P0502/503, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 309

Code P0502 will set if no vehicle speed is detected at start off. Code P0503 will set when vehicle speed has been detected and lost. Inspect all harnesses and related wiring, including VCM connectors.

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies normal charging system voltage is between 13.0 and 15.8 volts.
2. Checks actual battery voltage against voltage at VCM.

Code P0560, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 310

Code P0560, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 311

Charging battery with a battery charger and jump-starting engine may set this code. If code sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid and fusible link. Check for loose or damaged terminals at generator. Check belt tension and wear.

TCC brake switch input is used by VCM to determine when to energize TCC solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Checks brake switch.
3. Checks TCC brake switch signal at VCM.

Code P0703, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 312

Code P0703, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 313

Check customer driving habits and/or unusual traffic conditions, i.e. stop and go freeway traffic. Check brake switch adjustment. Check for most current VCM calibration software.

VCM sends a voltage signal to sensor and monitors return voltage. Transmission temperature sensor varies resistance as temperature of transmission fluid changes. Temperature sensor resistance is high when transmission fluid is cold. As fluid temperature increases, sensor resistance decreases.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for short to ground or sensor out-of-range.
2. Checks for an internal fault within transmission by creating an open.

Code P0712, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 314

Code P0712, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 315

After engine is started, temperature should rise steadily to about 212°F (100°C). Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

TEMPERATURE-TO-RESISTANCE VALUES

VCM sends a voltage signal to sensor and monitors return voltage. Transmission temperature sensor varies resistance as temperature of transmission fluid changes. Temperature sensor resistance is high when transmission fluid is cold. As fluid temperature increases, sensor resistance decreases.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Verifies a problem in sensor circuit.
2. Simulates Code P0712. If VCM recognizes low signal voltage, VCM and wiring are okay.
3. Checks 5-volt reference for open. There should be 5 volts present at sensor connector.

Code P0713, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 316

After engine is started, temperature should rise steadily to about 212°F (100°C). Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

TEMPERATURE-TO-RESISTANCE VALUES

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC when VCM commands TCC solenoid off. TCC slip speed should increase.

Code P0742, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 317

Code P0742, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 318

Check for proper TP sensor operation. If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply TCC, causing an engine stall.

Pressure control solenoid is used to regulate transmission line pressure. VCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. VCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of VCM to command pressure control solenoid.
2. Checks for voltage at VCM.

Code P0748, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 319

Check for poor connections at VCM and at transmission connector.

Voltage is supplied directly to solenoid. VCM energizes solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 1-2 shift solenoid and internal transmission for shorts.
2. Checks for power to 1-2 shift solenoid from ignition through fuse.

Code P0753, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 320

Code P0753, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 321

Check all connections at transmission. An open in ignition feed circuit can cause multiple codes to set.