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1998 Chevy Blazer P0446 Code: Diagnosis and Fix Guide

Model: 98 chevrolet blazer Fault Code: P0446 Posted: 2014-10-18 11:54

I own a 1998 Chevrolet Blazer that occasionally triggers several diagnostic trouble codes. After driving it approximately 50 miles to reset the system, the code returns consistently. At times, the check engine light stays off for hours before reappearing. I initially added fuel injection cleaner to the gas, which temporarily cleared some codes and allowed smooth operation. However, I now have a persistent P0446 code. I've thoroughly inspected all components including hoses, the fuel cap, and wiring connections. Despite this, I'm still unable to identify the root cause. The P0446 code indicates that the evaporative emission control (EVAP) system is not maintaining proper vacuum levels. This is a common issue in older Blazer models, especially due to aging or degraded components. The vehicle's service manual does not provide clear diagrams for certain EVAP parts, making visual identification difficult. I believe I've checked all accessible hoses and connections, but there may be an unobvious leak or malfunction. To confirm the system integrity, I need to verify whether the purge valve is opening and the vent valve is closing. Additionally, I should check if the fuel tank pressure sensor detects changes in vacuum — this data can typically be viewed on a diagnostic scanner as voltage fluctuations from the TPS (throttle position sensor). A smoke machine test would help detect any hidden leaks in the EVAP system, which remains one of the most reliable methods for identifying such issues.

Related fault codes

P0446

Comments (6)

Anonymous 2014-10-18 13:14

What specific components have you inspected so far? Have you checked the fuel cap, hoses, and vacuum lines?

Anonymous 2014-10-18 13:32

I've examined all EVAP hoses and connections. I suspect a faulty evap canister purge hose — it's located near the back left side under the hood. The factory service manual doesn't show clear diagrams for this area, so my diagnosis is based on visual inspection and experience. I’ve checked all fuel tank-related hoses and wiring. While the manual isn- t very detailed, I believe I've covered all accessible components unless they're in hard-to-reach areas. Thanks for the input!

Anonymous 2014-10-18 14:50

Have you confirmed whether the vent valve is closing properly? Is the purge valve opening? Has there been any recent work on the fuel pump? Are there any other diagnostic codes present? The system functions normally, including fuel gauge. This P0446 code is generic — it simply means the EVAP system cannot maintain vacuum pressure. In automotive repair practice, a smoke machine test is often used to visually detect leaks in the evaporative system.

Anonymous 2014-10-18 18:58

Yes, I’ve confirmed no recent fuel pump work and there are no other codes. The issue might be related to fuel mixture — using 87 octane may not be optimal for this engine, though I’m not certain. A dealer visit might be needed for further diagnostics. Thanks for the helpful suggestions! Initially, the auto store only mentioned it was a generic code, which I now understand is just a vague description.

Anonymous 2014-10-19 08:22

The term 'generic' here refers to the code's general nature — not that it’s part of a broad series like P0001–P0999. The P0446 code is set by the Powertrain Control Module (PCM) when the vacuum decay rate exceeds a threshold. To diagnose properly, we must confirm: 1) purge valve opens, 2) vent valve closes, 3) fuel tank pressure monitor detects pressure changes — then proceed to look for leaks. A smoke machine test is the most effective tool for identifying such issues.

Anonymous 2014-10-19 14:20

Ah, I understand now! Thanks so much. I'm still in the process of troubleshooting and have reset the code after our last discussion. I’m currently driving it to see if the P0446 returns — it may come back by Thursday when I get a chance to test further. As someone new to car repairs, this has been quite challenging. I originally bought this later-model Blazer thinking it would be easier to maintain myself, but it’s turned out to be more complex than expected. I appreciate all the advice and will provide an update soon!