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Old 06-11-2016
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Join Date: Jun 2016
Location: Riverside, ca
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98 Ranger 2.5l 4x2

Check engine light on. OBDII (forget code) indicated oxygen sensor. I replaced both. New OBDII code read P0171. I replaced MAF, TPS, IAC, and PCV. Cleaned throttle body. Replaced #2 sparkplug wire (it was bad). New code reads P0122. DVOM reads 5.1 volts when testing TPS. I'd replace the EGR if I could reach the flange nut on manifold tube.

What's next?
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Old 06-11-2016
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Join Date: Jan 2014
Location: Vancouver, BC
Posts: 7,606
Welcome to the forum

First thing you need to know is that OBD codes are not literal, they are a loose translation of computer binary code.
So there is no "bad sensor code".

For example P0171 means computer has added more fuel than it thinks is reasonable and O2 is still reporting higher than normal oxygen in exhaust.
We call it a Lean code in english, but engine is/was never running Lean.
O2 sensor not switching, could mean O2 sensor wiring or O2 sensor itself, but 90% of the time it is fuel mix issue, related to P0171, lol.

And the 90% is another number to remember.
90% of all sensors and controls(like the IAC) replaced by DIYers were working fine.

In fact, any code that mentions a sensor in its english translation usually means that sensor is working or computer wouldn't know there was a problem.
So "don't shoot the messenger" based on code number

TPS sensor has 3 wires
5 volt in from computer
1 volt out to computer

What you should do is to get a sewing pin to test new TPS
Pierce the center wire on TPS
Turn on the key and test its voltage
.69-.99volts is spec, under 1 volt with throttle closed
If you are under .69v then loosen TPS and move it slightly to raise voltage, then tighten it up

Now open throttle slowly and voltage should go up, no jumping around or dropping down.
At wide open throttle voltage should be above 4.5 volts, 4.51-4.99volts is spec

TPS is a Learned sensor, IAC Valve is a Learned control
When you change these it will take the computer a few Drive Cycles to relearn the voltages.
1 Drive cycle = full warm up and cool down

Last edited by RonD; 06-11-2016 at 03:14 PM.
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Old 06-11-2016
Thread Starter
Join Date: Jun 2016
Location: Riverside, ca
Posts: 2
Thanks. Replaced parts this week. Have only driven truck around the block.
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