Archive for the ‘Auto Care’ Category
Throttle Position Sensor Diagnostic Tip
The throttle position sensor is another computer sensor that is often misdiagnosed. Popular replacement TPS sensors are available at the bottom of this page but please test your old one before replacing it.
What should you do if you find a TPS sensor code set in the computer’s memory. Both professional and DIY auto mechanics will often replace the component just because the code has set.
As I have learned in the school of hard knocks, just because a sensor has set a code does not mean that the part has failed. The sensor may be trying to tell you the truth and other related wiring problems could actually be causing the malfunction.
The TPS sensor is a potentiometer type of electrical component. Rather than just being opened or closed like a switch, the TPS controls the circuit by varying its resistance in response to throttle position.
In most cases, this sensor will send a very low voltage back to the vehicle’s main computer when the throttle plates are fully closed. This reference voltage increases as the throttle plates are opened. Some manufacturers use inverse voltage readings for feedback.
A bad part can cause many problems in the vehicle’s overall performance. Inaccurate data can cause transmission problems as well. Some of the conditions related to TPS sensor problems can be no up shifting, fast up shifts, late or delayed shifts, and line pressure problems that control internal solenoids and torque converter clutch engagement.
You can test a throttle position sensor with an automotive scan tool. This is probably the easiest and most cost-effective way to diagnose a TPS problem. Although the scan tool will have to be capable of displaying the data stream. Some of the cheaper scan tools only read and erase check engine light codes. The TPS value can be analyzed on the scan tool and the throttle slowly depressed looking for either increase or decrease in voltage. Any dead spots or opens in the potentiometers will show up as a momentary flash of 0 V on the scanners data stream.
You can also test this computer sensor with an automotive meter.
You’ll most likely need a wiring diagram to identify the output voltage wire that goes to the vehicle’s main computer. Back probing the lead will provide a voltage value, as you to press on the throttle Slowly. Again a dead spot in the throttle position sensor will show up as zero voltage as the dead spot is engaged.
Professional mechanics prefer testing this component with a Lab scope. The waveform can be displayed on the scope display in real time and the DC signal monitored as the throttle is opened and closed. The voltage output of a Tps sensor will typically range from .5 V to 4.5 V at wide-open throttle.
Change in voltage should be smooth with no dead spots or spikes. Looking for a glitch in the signal is easiest with a Lab scope. But can be performed with both the scan tool and a voltmeter as described above. In most cases, a replacement TPS sensors is considered an electrical component and is not returnable. If your vehicle has set a code for a throttle position sensor takes the time to perform some tests before replacing the nonrefundable electrical car part. When it comes to the fastest way to a repaired vehicle, following a diagnostic chart for the specific code set for your vehicle is highly recommended.
Factory service manuals provide the highest quality diagnostic repair diagrams. For more information about online repair diagrams see my video of inexpensive, downloadable factory auto repair manuals.
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What You Need To Know About Grease
Q: I shot a bunch of expensive marine-style grease into the bearing buddies on my bass-boat trailer last fall. It was recommended to me by a marine mechanic as the best product for my trailer, because the wheels get dunked regularly, and this particular type of grease is supposed to be more water-resistant. I finally got a chance to go fishing last weekend and noticed that the grease cups had all leaked oily snot all over my brakes. So instead, I spent the afternoon cleaning and repacking all six wheel bearings and replacing all of the greasy, oily brake shoes. Can you suggest a brand of grease that won’t do this?
A: You mentioned the brand of grease in your letter, which I removed, because it’s a perfectly good product, and the correct one for your application. Specifically, i t ‘ s an aluminum-complex grease, and this type of grease has excellent performance when there’s a chance of water contamination, like on your trailer.
A primer about grease: It’s basically nothing more than a heavy oil mixed with enough soap to make it stringy and clingy enough to remain in place as the bearing spins. This will ensure the bearing’s rollers or balls are constantly covered in the oil. The soap is based on a variety of compounds, notably lithium or aluminum complexes for most of the greases used in cars, trucks and boats.
Problem: Not all the soaps are compatible with each other. This causes the soap and the oil to separate, letting the latter settle to the bottom of the cavity the bearing is in. No surprise—a lot of grease caps have a poor metal-to-metal seal and will let the oil leak out after some weeks. Like yours did.
Your wheel bearings were probably originally lubed with a lithium-12-complex grease, a perfectly good grease for wheel-bearing use, even on a boat trailer if it’s maintained. Shooting some more grease into the bearing cap with a grease gun isn’t a bad idea. Shooting an incompatible grease in is.
This counterpoints the need to completely remove the last vestiges of old grease from a bearing whenever it’s repacked. Yes, you want to remove the dirt and wear particles, but odds are you won’t know what kind of grease the last mechanic used.
I’m not going to print a huge grease compatibility chart here, although that kind of information is available on the Internet. If you always clean the bearings properly before repacking, it will never be a problem.
Don’t have a nice parts-washing sink with recirculating solvent handy to your driveway? It’s still easy to clean the bearings properly. Remove the bearings, inner and outer, and any shims, lockwashers and clamp nuts. The bearing inner or outer races can stay pressed in place, however. Scrub the inside of the bearing cavity with paper towels until you’ve got as much grease out as possible, and wipe as much off the bearing itself. Dump the used paper towels. My favorite bearing cleaner for the field is a disposable aluminum pie tin, but any suitable vessel will do. One at a time, clean the parts in solvent, whether it’s turpentine, paint thinner, kerosene or even hot, soapy water in a pinch. Keep the bearings separate so they go back into the same wheel-don’t mix and match. Use a cheap disposable paintbrush to scrub all the old grease out. Let dry, then finish with a quick blast of carb or brake cleaner to get the last dust off. If you have compressed air, you can use it to dry the bearings as long as you don’t spin them into destruction. Pack the bearings by hand, and fill the cavity approximately halfway with grease.
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