Page 6 (Updated 28-Nov-08)
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TPS Throttle Position Sensor
- Overview
- TPS Assembly Parts
- Potentiometer Repair
- Opening the Assembly
- TPS Tests and Adjustments
Free Service Manual, Free Download.....see FAVORITE LINKS -page 26- FAVORITE LINKS
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Overview
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TPS contains two separate entities in one box: One is a slider potentiometer giving accurate throttle axle angle information to ECU. Second functionality is the zero position & 2/3 throttle switches.
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TPS Location at the end of Throttle Body (TB)axle. Note that the TPS assembly has TWO connectors. One is attached in the base plate at TPS box end - the zero position switch (blk) connecor. The other, wire & connector (grey) is for the Position Potentiometer.
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When TPS becomes suspect, it has first to be tested. Note that the Manual states that TPS switches are NOT used (it says that only diagnostics uses Zero postion sw).
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TESTING:
TPS Assembly, its Potentiometer and Switches may be tested in four 4 ways :
Stand-Alone tests:
1. Zero Position Alignment with multimeter at TPS, both TPS connectors disconnected, see below.
2. Resistance tests
3. Circuit/Voltage test with multimeter at TCU; connectors installed, see below .
System wide Diagnostics:
4. With TCU -Test Program: Utilizing Automatic Transmission Self Diagnostics -procedure, systemwide functionality test. Built-in Diagnostics with ten stages contain also TPS test; refer to TCU self diagnostics at page 21 . as this (4 test) is not explained on this page
Note: One of the many prerequisites for successful TCU-Self Diagnostics, is a functional TPS zero -position Switch.
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Assembly Parts
TPS Functional entities explained:
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The two connectors, main adjustment/attachment screws. At right: Zero Postion and 1/3 throttle switch functions.
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At left, the red cam /Potentiometer-slider. At right is seen the card on the base plate, on it is etched the Position Potentiometer resistor slider surface. Here the slider has been taken out; check the surface for continuity.
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The red potentiometer slider attaches to the throttle axle via a axle fitting (picture above). In the red plastic slider facing the potentiometer surface -card, there is attached a metal slip. It has two contact-brushes connected in both ends, sliding on the potentiometer resistors two surfaces as throttle axle rotates. On the opposite side of this red plastic slider, there are the cam grooves followed by the zero & 1/3 throttle position switch 'cams'.
TPS Potentiometer slider brush assy with brushes on both ends (one contiguous metal part) seen from the side facing the potentiometer -card.
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Potentiometer 'Repair'
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Fast Track 'repair' - only for intermittent Potentiometer problems related with soot or water inside:
One of the possible reasons for malfunctioning TPS is accumulating soot worn off from the resistor surface and/or water after engine powerwash. This might be cleaned by making a hole on the box corner for example with a solder iron tip [no drilling], and flooding the box with electronics contact cleaner. Best place for the hole is in the corner as there is more room than top (see the red switch guide inside).
During flooding the throttle should be moved back and forth. After that let it dry, close the hole with sealant.
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Making the hole in the corner (yellow arrow) and spraying cleaner in.
The spray should hit the top of the resistor -card surface inside the assy to clean it. Aim top center as the arrow indicates.
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Afterwards close the hole with silicon or liquid seal.
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Opening the Assembly
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The assembly is factory sealed and not built to be serviced or opened. Next the sturucture is depicted for DIY service.
If the problem is mechanical, most probably the potentiometer slider brushes have to be re-aligned as was in my case. One would think that the resistor surface itself wears out, but at least on this 80k engine no wear could be detected.
Drill the rivets out from assembly bottom plate to get the plastic blk cover off. Next main axle locking washer is been cut/grinded to be snapped out. Then the base plate -supports for the switch connector are grinded out to disconnect it from the base plate.
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Baseplate with Potentiometer -card & wire, beside lock washer is the slider tightening spring washer. At right is seen the base plate from opposite side and the blk plastic cover.
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Re-installation: extra O-ring, cover glued to shield from moisture
TPS Connectors from the ECU. Nearby tubing definitions, Right: the finished installation.
TPS Electrical connections to the ECU
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Btw. Its easier to buy (90$) new... but still that haybox should be sealed before installation.
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Tests and Adjustments
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Three TPS stand-alone tests and adjustments
...engine OFF, both TPS connectors opened, refer to pics above:
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What FSM says about the Switches 1? It calls it "the Hard closed throttle position switch; It is not used in engine control but only for on-board diagnostics system ... switch 2 is not used at all" see EF&EC p.12. ... Have fun: Next the Automatic Transmission FSM page AT-12 contradicts this statement.
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1. ZERO -POSITION switch adjustment, -test at TPS:
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Install new/repaired TPS to Throttle body TB, hand tighten screws. Take multimeter (ohm scale or 'buzzer') and measure from opened connector from TPS box back, mid and top pins. There has to be constant connection on the two pins as throttle is closed. When throttle is slightly turned, the contacts have to open. If this doesn't happen, assembly needs adjustment (rotate a bit).
Tighten screws, recheck. Perform Idle adjustment. (Note that throttle body /butterfly flaps zero position is not affected, for that refer to previous pages.) See IACV, page 4.
MID and LOWER pins for the "2/3 throttle": This switch is NOT used anywhere.
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2. POTENTIOMETER Resistance -test at TPS
- Measure with a multimeter, ohms scale, the TPS potentiometer disconnected:
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What FSM says about the Potentiometer? It calls it "Soft closed throttle position switch (Potentiometer); voltage signal to ECU. see FSM EF&EC p.12
The second TPS box wire connector (grey) is for the potentiometer. It should give readings between 1kOhm-9kOhm as throttle is moved to WOT = wide open throttle. Linear response is important.
Measurement between MID and one connector pin gives reading 1-->9kohms and second measurement between MID and second connector pin gives 'mirror' reading 9-->1kohms as throttle is opened/closed.
My TPS (as some new ones might be) was 2½k-11kOhm before repair, most important is that its 'giving' constantly linear readings, no breaks in reading. (On VG30DE engine this potentiometer resistance is around .5k-5kOhm)
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3. CIRCUIT/VOLTAGE TEST WITH MULTIMETER - at TCU
Voltage testing - NOW all TPS connectors are now connected.
- Ign OFF - Open plastic kick panel beside gas-pedal. Take white TCU connector shield off to access connector pins. All Connectors stay connected. (refer to page 15. )
- See the tst cable guide below. Turn DMM to DC Voltage scale, insert one DMM probe via your test cable into TCU connector pin 34 and other to GND = pin 48. DANGER: before installing probes, make absolutely sure that they will not make contact and make a short circuit.
- Now turn Ign ON [engine off]
- Pedal is up; reading is 0.2-0.6 Volts.
- Push pedal slowly; reading rises to 2.9-3.9V. Release pedal back up; reading goes back to 0.2-0.6 Volts. ... TPS potentiometer is ok.
- Start engine and verify healthy charge voltage: 13.5V minimum
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Building a TPS / TCU Transmission Control Unit -test cable:
(refer to page 15. )
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At Left, three test wires attached to TCU connector: Pin4 = Power supply, Pin48 = TCU Ground, Pin35 = TPS signal. Location Note: the gas pedal seen in front...
At right, a paper clip test pin has been pushed inside the TCU connector from rear.
Connect/Solder the three spare wires into sharpened pins (paperclips?), wire length 3 feet or more. Push clips into the TCU connector from rear as shown above. Then the free wire ends are screwed into a screw terminal block. Use tie wraps to fix the test wires. Attach your multimeter to terminal block ground, then to the signals to be tested, measure with ign at ACC -or- engine running.
You may also add more signals and use LED's to indicate the various status signals. Buy LED's and solder in series with 390(or 600) ohm resistors, solder & build your 'test bench'. I soldered a 18-wire test harness direct into the TCU cable, added the connector with LED's to troubleshoot A/T solenoids etc. signals. Make sure no shorts will occur; this setup is dangerous...
Do not utilize a test led into transmission speed sensor, it overloads the circuit.
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Now you may go for a test ride. Secure the test settings first so that objects will not become loose, digital multimeter easily readable...
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Comment:
If you get good test results from the potentiometer, do not think that the potentiometer still is always ok. The sliders are (maybe) flying on the resistor residue soot, and they are just playing games with you. This totally incomprehensible construction is std on most cars nowadays, but somehow we users have to sputter on with them.
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Matthews 'TPS guide': Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof. But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.
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