DTC P1780: PARK/NEUTRAL POSITION SWITCH CIRCUIT Toyota Tundra I

Circuit Description

Test applies only models with automatic transmission. Park/Neutral Position (PNP) switch delivers input signals to ECM. Input signals are used for air/fuel correction and for idle speed control. DTC is set when 2 or more switches are on simultaneously for "R", "N", "2" and "L" position or when ECM is receiving an ON signal from PNP switch when vehicle is being operated for more than 30 seconds at 44 MPH or more with engine speed of 1500-2500 RPM. Possible causes are

1. PNP switch circuit is shorted.
2. Defective PNP switch.
3. Defective ECM.

Diagnostic Aids

Using hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.

Scheme 265

1. If using Toyota hand-held tester, go to next step. If Toyota hand-held tester is not available, go to step 6.
2. Connect hand-held tester to Data Link Connector (DLC) No. 3. see scheme 1 Turn ignition on and then turn hand-held tester on. Using hand-held tester, monitor PNP, REVERSE, 2ND and LOW signals while moving shift lever into Park, Reverse, Neutral, "2" and Low. Ensure signals are properly displayed in relation to shift lever position. See «INPUT SIGNAL DISPLAYS»(ref-63532-S42720563572001073100000) table. If signals are not properly displayed, go to next step. If signals are properly displayed, replace ECM. ECM is located behind glove box and heater duct. see scheme 2 INPUT SIGNAL DISPLAYS Shift Lever Position Signal Display Park & Neutral PNP OFF-ON Reverse REVERSE OFF-ON Low LOW OFF-ON 2 2ND OFF-ON
3. Disconnect electrical connector from PNP switch. PNP switch is located on side of transmission. Note PNP switch terminal identification. (Scheme 265) Using ohmmeter, check for continuity between specified terminals with shift lever in proper positions. See «PARK/NEUTRAL POSITION SWITCH SPECIFICATIONS»(ref-63532-S41365512522001073100000) table.
4. If proper continuity exists, go to next step. If proper continuity does not exist, adjust or replace PNP switch as necessary. For adjustment or replacment procedures for PNP switch, see PARK/NEUTRAL POSITION SWITCH under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article. PARK/NEUTRAL POSITION SWITCH SPECIFICATIONS Shift Lever Position Continuity Between Terminals No. Park 1 & 3; 6 & 9 Reverse 2 & 3 Neutral 3 & 5; 6 & 9 Drive 3 & 7 2 3 & 4 Low 3 & 8
5. Check wiring harness and electrical connectors between PNP switch and ECM, and between battery and PNP switch. See WIRING DIAGRAMS article. It may be necessary to consult wiring diagram in appropriate STARTERS article in STARTING & CHARGING SYSTEMS for additional PNP switch wiring. ECM is located behind glove box and heater duct. see scheme 2 Repair wiring harness or electrical connectors as necessary.
6. Remove glove box and heater duct (if necessary) for access to ECM with electrical connectors still installed on ECM. see scheme 2 Turn ignition on. Using voltmeter, check voltage between body ground and specified terminal at ECM electrical connector E4 in relation to shift lever position. See «PARK/NEUTRAL POSITION SWITCH VOLTAGE»(ref-63532-S33812623622001073100000) table. see scheme 4 If voltage is not within specification, go to next step. If voltage is within specification, replace ECM. PARK/NEUTRAL POSITION SWITCH VOLTAGE Shift Lever Position Terminal No. Volts Park & Neutral 2 (1) 0 3 (1) 0 12 (1) 0 20 (1) 0 Reverse 2 (1) (2) 7.5-14.0 3 (1) 0 12 (1) 0 20 (1) (2) 9.0-14.0 Drive 2 (1) 0 3 (1) 0 12 (1) 0 20 (1) 9.0-14.0 2 2 (1) 0 3 (1) 7.5-14.0 12 (1) 0 20 (1) 9.0-14.0 Low 2 (1) 0 3 (1) 0 12 (1) 7.5-14.0 20 (1) 9.0-14.0 (1) Measure voltage between ground and terminal listed at ECM electrical connector E4. see scheme 4 (2) Voltage may be slightly less due to illumination of back-up lights.
7. Disconnect electrical connector from PNP switch. PNP switch is located on side of transmission. Note PNP switch terminal identification. (Scheme 265) Using ohmmeter, check for continuity between specified terminals with shift lever in proper positions. See «PARK/NEUTRAL POSITION SWITCH SPECIFICATIONS»(ref-63532-S41365512522001073100000) table.
8. If proper continuity exists, go to next step. If proper continuity does not exist, adjust or replace PNP switch as necessary. For adjustment or replacment procedures for PNP switch, see PARK/NEUTRAL POSITION SWITCH under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
9. Check wiring harness and electrical connectors between PNP switch and ECM, and between battery and PNP switch. See WIRING DIAGRAMS article. It may be necessary to consult wiring diagram in appropriate STARTERS article in STARTING & CHARGING SYSTEMS for additional PNP switch wiring. Repair wiring harness or electrical connectors as necessary.