2000 Olds Alero DTC Codes

[tblake]

Hey Guys,

2000 Olds Alero, 100,000 miles, 3.4V6.

I have 3 DTC codes.

P0122 - Throttle Position Sensor Circuit Low Voltage

P0440 - Evaporate Emission System

P0442 - Evap System Small Leak

I have a spair TPS sensor I am going to swap on there. In fact that code is not the one that scares me.

Its the emission ones. P0440 defenition is vague. I bought a used gascap from a junkyard that I am going to put on there, clear the codes, and see what comes back.

I am just wondering if anyone can tell me about any common issues.

Also, does anyone know what the TPS sensor wires are supposed to do at the plug? Which one is ground, which one is the signal, and which one is B+ and is the B+ wire 5v or 12v?

Aside from those issues, I have the "trac off", "ABS", Low Tire Pressure", and Service Vehicle Soon" lights on.

Any suggestions? I have not really had a chance to mess with it yet.

[old_master]

P0122 = low voltage returned from throttle position sensor. Could be a sensor or wiring problem. Grey with black tracer is reference voltage 5VDC. Black is sensor ground, should be less than 5 ohms to ground. Dark blue wire is signal wire to PCM. Should be ~ .5VDC when throttle is closed, and smoothly go to reference voltage when opening throttle to wide open.

P0440 along with the P0442 = EVAP system malfunction. Could be most anything from the fuel cap, filler neck, vent line, vent solenoid, purge solenoid, purge canister, fuel tank, or any of the lines that connect them together.

The trac off, ABS, and tire pressure could all be related to a faulty wheel speed sensor. You need to have the EBCM scanned for codes.

Unless you have definitely confirmed a faulty part, stay away from the boneyard... it's like the proverbial box of chocolates, you never know what you're gonna get.

[tblake]

Originally Posted by old_master

P0122 = low voltage returned from throttle position sensor. Could be a sensor or wiring problem. Grey with black tracer is reference voltage 5VDC. Black is sensor ground, should be less than 5 ohms to ground. Dark blue wire is signal wire to PCM. Should be ~ .5VDC when throttle is closed, and smoothly go to reference voltage when opening throttle to wide open.

P0440 along with the P0442 = EVAP system malfunction. Could be most anything from the fuel cap, filler neck, vent line, vent solenoid, purge solenoid, purge canister, fuel tank, or any of the lines that connect them together.

The trac off, ABS, and tire pressure could all be related to a faulty wheel speed sensor. You need to have the EBCM scanned for codes.

Unless you have definitely confirmed a faulty part, stay away from the boneyard... it's like the proverbial box of chocolates, you never know what you're gonna get.

Wonderful on the Emission codes!! Thats what I expected to hear I guess.

And your right about the boneyard, but its good for odds and ends.

Thanks for the TPS wiring info, I'll grab a multimeter and see what I have.

[BNaylor]

Tim,

In order to set the TPS P0122 DTC the TPS signal voltage (output) would have to be less than .1 volt. If the PCM 5v reference is good and you have adequate output at the low reference signal back to the PCM module (1-4 volts) varying the accelerator be sure to check the wiring to the PCM module at the two 80 pin connectors.

TPS Dark Blue wire goes to pin 66 of connector C2. TPS Black wire to pin 61 of C1. See thread below for PCM related work and location.

Click here

Best to resolve the TPS issue first before working on the others. Also, what is common to the evaporative emissions DTCs is the PCM module and same electrical connectors. Check the fuel tank pressure sensor signals. Good luck!

[tblake]

Thanks Bob, I was wondering that.

The FSM says to connect a scan tool, jumper the 5v reference wire to the signal wire, and turn ignition on. If the scan tool reads 5v on the TPS, the reference and signal wires are good. Then it says to check the resistance of the ground wire to a known good ground.

I think I'll hook up my powrtuner and see what its doing. I wonder if I can watch EVAP systems with it too. Something tells me I can. I bet I can ever watch wheel speed sensor and find out what hub is bad.

I have all this time to diagnose in my head, but limited time to diagnose hands on.

[BNaylor]

Originally Posted by tblake

I bet I can ever watch wheel speed sensor and find out what hub is bad.

It could be a hub(s) but on Aleros or Grand Ams check out the electrical connector at the hub and the wiring where it runs along the lower control arm and then the subframe. Then check the big electrical connector at the ABS Motorpack/EBTCM module located on the front left side (driver's) of the subframe. Subject to corrosion.

[tblake]

So I changed the gas cap over, checked the TPS connector. It has good power 5v, and a good ground, so I just swapped on my spair TPS sensor and cleared all the codes.

Then I took it for a spin. TPS light stayed off. WHen I got back I hooked up my code reader again and P0440 was pending. But the P0442 and P0122 were gone.

How should I diagnose P0440? It may just be one of those things I live with. Where are common leak spots on the evap system on alero's? Does O'reilley's or Advnace rent out smoke machines?

[old_master]

P0440 = EVAP system malfunction. Could be most anything from the fuel cap, filler neck, vent line, vent solenoid, purge solenoid, fuel tank pressure sensor, purge canister, fuel tank, or any of the lines that connect them together. The most common cause is a worn out O ring on the fuel fill cap, did you replace the cap with a new one?

[tblake]

Thanks for the info.

I replaced the cap with a used salvege yard one. I want to keep costs as low as possible on this car. Seems odd that two caps would have the same issue. I read a TSB where the o-ring on the sending unit in the fuel tank causes p0440 issues.

I wish I had a smoke machine......

I may just live with the P0440 for now. I think I'll focus on the Trac off, Low Tire Pressure, and ABS lights now.

[old_master]

Originally Posted by old_master

Unless you have definitely confirmed a faulty part, stay away from the boneyard... it's like the proverbial box of chocolates, you never know what you're gonna get.

Leaky fill cap O ring is very common, so it's very possible you got bad one. New AC Delco caps are not all that expensive.

[tblake]

Ok, I will pick up a new one. I just question ac-delco/GM parts quality recently. Plus my experiances is that its never an easy fix (ie gascap replacement). I wonder if the gascap is the same partnumber on my GTP. I could swap the two. I know mine is good.

A smoking of the EVAP system would prove where the leak is, if there is a leak, and not a sensor problem. I should hook up my tuner and see if I can watch the fuel tank MAP sensor reading.

Either way I could eliminate the code once and for all by just deleting it out of the PCM, so I dont know how much money and time I want to spend on diagnosis.

[tblake]

"We'll give you something to cry about
November 6, 2012
You're next!"

I love it!

But check this out. Today I hooked up my powertuner. Its capable of reading extended GM service codes. P0440 didn't show up. But another one, P1189.

P1189 - Engine Oil Pressure (EOP) Switch Circuit

Does the PCM in this car really monitor oil pressure? All I know is that the Oil pressure light on the dash is there, and is not on. Plus I drove this car all the way home (40 miles) and it is running just fine.

Is this code just a fluke, and where is the oil pressure sensor?

[old_master]

The PCM gets that data from the oil pressure sending unit. The same switch that turns on your oil light. The switch is calibrated to close the contacts when pressure drops below about 7psi. Might want to check oil pressure with a gage, just to be on the safe side. If oil pressure is within specs, I wouldn't worry about it. Was the SES light on? Was the DTC a hard fault, pending fault, or in the history file?

[BNaylor]

Tim,

I would not depend on the DHP Powertuner for odb-ii diagnostics or how did you modify it? Best to use a good ole odb-ii scanner/scan tool with GM extended codes capability.

BTW - Just in case I have a spare PCM module but for a '02 Alero with 3.4L. Service ID may match.

[tblake]

Originally Posted by old_master

Was the SES light on? Was the DTC a hard fault, pending fault, or in the history file?

I will check oil pressure, but doesn't that code point towards a circuit problem?

The SES light was not lit, I think it may have been a hard fault but since its a type 3 it didn't illuminate the SES light. (funny how something as inportant as oil pressure wouldn't light the ses light, but I suppose there is a second light)