94 Explorer coding p0172, p0176

[courtjester]

What would cause my 94 Explorer to throw OBD2 codes: P0172, P0176, and P0332? What do they all have in common? Just changed the alternator. Someone told me it could be the fuel pump or the ignition switch, but IDK.

Symptoms: Sometimes has a rough idle with fluxuating voltage and will shut down, will sometimes lose power when trying to gain speed, sometimes chokes down when trying to take off from a stop, and sometimes tries to lunge intermittently when at cruising idle.

 

[Iron Weasel]

DTC 172
Lack of heated oxygen sensor switches indicates lean (bank # 1).

DTC 176
Lack of heated oxygen sensor switches, indicates lean (bank #2).

DTC 332
Insufficient exhaust gas recirculation flow detected.
Diagnostic Trouble Code (DTC) 332 indicates the Pressure Feedback EGR (PFE) / Differential Pressure Feedback EGR (DPFE) sensor signal to the Powertrain Control Module (PCM) did not change when the PCM output a duty cycle to the EGR Vacuum Regulator (EVR) solenoid requesting EGR flow.

Humor me on this one.... Have you changed your oil lately? If it's been a while, you might want to change it. Believe it or not, "Diluted engine oil" can cause 172 & 176 to be thrown. If you've changed your oil recently, then you'll want to check and make sure your PCV valve is connected to vacuum and is working. Easy way of checking it is to pull the hose off the valve, pull the valve out and shake it. If it makes noise, it's OK.

If your PCV valve is good, you'll need to grab a fuel pressure gauge and check your pressure. The fuel pressure should be 30-45 psi KOER (Key On, Engine Running) and 35-45 psi KOEO (Key On, Engine Off). If the pressure is in range, turn the key off and see if the pressure remains steady. A couple PSI drop is OK, like 1 - 3 or so, but if it drops 5+ PSI within a minute, you have a problem.

As for 332, it can be caused by a few things:

Obstructed EGR passages
Vacuum hose leaks.
Obstructed vacuum hoses.
Damaged EVR solenoid.
Damaged PFE/DPFE sensor.
Damaged EGR valve.
Damaged PCM.

For this one, you'll need a vacuum gauge. You want to disconnect the vacuum hose at the EGR valve and connect the hose to a vacuum gauge. After you have everything hooked up, you need to run the KOER Self-Test. While it's running there should be vacuum. If the gauge doesn't move or barely moves, check the vacuum line going to the EGR Vacuum Regulator. If you've got 15 Hg or more on the input to the regulator, then you have a bad Differential Pressure Feedback EGR (DPFE) sensor. If you get decent vacuum during the KOER Self-Test, post back up and I'll give you the rest of the steps.

 

[courtjester]

Could not having the Vapor Canister Purge Solenoid installed cause this?

 

[Iron Weasel]

Could not having the Vapor Canister Purge Solenoid installed cause this?

Yeah, the solenoid is listed as one of the possible causes of the 172 & 176 DTC's but it's probably a separate issue than what's causing the 332 DTC to pop up.

If you still have the solenoid laying around, reinstall it and clear the codes out of the PCM then drive it around like normal and see what codes (if any) come back up.

Here are the lists for the DTC's, just so you have a reference point:

172 & 176
Fuel injectors.
HO2S.
Secondary Air Injection (AIR) system.
Positive Crankcase Ventilation (PCV) /Hose.
Vacuum.
Evaporative Cannister Purge.
Manifold Absolute Pressure (MAP) sensor.
Electronic Ignition Coil Failure.

332
Icing
Obstructed EGR passages
Vacuum hose leaks.
Obstructed vacuum hoses.
Damaged EVR solenoid.
Damaged PFE/DPFE sensor.
Damaged EGR valve.
Damaged PCM.

 

[courtjester]

The canister purge solenoid was on a vacuum hose... the tubes on the nipple were broken off when my husband replaced the head gaskets. He pushed a screw into the end of one hose and clamped off the other till we can replace the solenoid. Which is why I was wondering if this could be the vacuum hose that might be leaking. Or obstructed.

 

[Iron Weasel]

To answer one of your original questions - What do all the codes have in common? They're all related to the emissions control system.

If you have a vacuum leak after the MAF sensor, like where the purge solenoid hose enters the intake manifold, then it would cause unmetered air to enter the engine and the PCM won't be correcting the fuel flow, which would cause a lean mixture. Personally, I'd replace the purge solenoid and vacuum lines then clear the PCM and see if any codes are set again.

 

[courtjester]

Ok, thanks. I'm ordering a new solenoid and we'll see if that fixes things. I greatly appreciate the help!

 

[westfield]

I thought 94 was OBD 1 ?

 

[Iron Weasel]

I thought 94 was OBD 1 ?

It's OBD 1.5

It's not OBD-II compliant since that didn't go into effect until 1996, but it has more "features" than the older EEC-IV system that was pretty much Ford's version of OBD-I. The EEC-IV on the 94 system monitors some emission components, but not to the extent that an OBD-II system would.