1989 Toyota 22RE: Idle Dying, Check Engine Codes 25/51/71, and the Circuit Opening Relay

What those symptoms are actually telling you

Three check engine codes, an engine that wants to die at idle, and a clicking noise near the passenger dash sound like a mess. On a 1989 Toyota pickup with a 22RE, they tell a fairly coherent story once you know how the fuel and emissions systems work on these trucks.

Breaking down codes 25, 51, and 71

The 22RE uses a simple blink code system built into the ECU. To read codes yourself, locate the check connector — a small black plastic box under the hood — and short the TE1 and E1 terminals with a jumper wire. Count the flashes on the CEL: long blinks are the first digit, short blinks are the second.

Code 25 is a lean air-fuel mixture condition. The ECU is reading an O2 sensor signal indicating the engine isn’t getting enough fuel relative to incoming air. On the 22RE the usual suspects are a lazy or failing oxygen sensor, a vacuum leak (the large intake boot between the airflow meter and throttle body cracks with age, as does the intake manifold gasket), low fuel pressure, or a faulty fuel pressure regulator. A mechanic observing that the engine is “running a little lean” matches this code exactly.

Code 51 relates to the A/C switch or idle-up signal circuit. On trucks without air conditioning, it can set if that circuit is open or the idle-up actuator isn’t responding as the ECU expects. It’s not a primary driveability code — it affects how the ECU compensates idle speed when accessories draw load.

Code 71 is an EGR system malfunction. The EGR valve itself can stick open or closed, its vacuum supply lines crack with age, and the EGR temperature sensor fails over time. A stuck-closed EGR rarely causes noticeable driveability problems in everyday use, but it keeps the check engine light on and will cause a smog test failure in states that check OBD-I codes.

The clicking near the dash: it is not a speaker

This trips up a lot of people unfamiliar with the 22RE. There is no speaker in that passenger footwell location. What’s mounted there on these trucks is the Circuit Opening Relay — commonly called the COR.

The fuel pump on the 22RE does not run continuously. The ECU controls pump power through the COR. When the engine cranks, or when the ECU sees a signal from the airflow meter confirming the engine is running, the relay closes and the pump runs. When the COR begins to fail — especially under heat — it chatters as the contacts open and close rapidly. That is the clicking sound.

An intermittently failing COR cuts power to the fuel pump. Fuel pressure drops, the mixture goes lean, and the engine stumbles toward stall. Blipping the throttle masks it because the added airflow signal briefly holds the relay closed. At a true idle with no throttle input, the engine dies.

If the mechanic replaced “the relay,” it is worth confirming he replaced the Circuit Opening Relay specifically. The COR and the main fuel pump relay are separate components that do different jobs. Swapping one when the other is faulty solves nothing.

Why the problem appeared when it did

Electronic components on a truck this age often fail thermally. They work fine cold, fail when hot, and sometimes recover once the engine cools. The COR is a documented weak point on the 22RE for exactly this reason. Running in high ambient temperatures while carrying a cabover camper puts extra load on the drivetrain and tends to raise under-hood temperatures — enough to push a marginal relay over the edge when it was previously hanging on.

The fuel pump itself can exhibit the same pattern. As brushes wear, the motor draws more current, generates more heat, and fails hot. A practical field check: if the engine dies and you let it sit for 20 to 30 minutes until it cools, then it starts right up again, you are dealing with thermal failure rather than a hard mechanical problem. That narrows the suspect list considerably.

A logical diagnostic sequence

Start with a fuel pressure test. Confirm adequate pressure at idle, then check pressure hold after shutting off the pump. Quick pressure drop after shutoff can indicate a leaking injector or a failing fuel pressure regulator — both of which also produce a lean condition and contribute to code 25.

If fuel pressure checks out, verify power at the fuel pump while the engine is running, then again while it’s stumbling. Loss of voltage to the pump during the stumble points directly at the COR.

The oxygen sensor on a 1989 truck has a lot of miles on it. A slow or contaminated sensor feeds inaccurate data to the ECU, which then cannot properly correct the mixture, and code 25 keeps coming back. Replacing the O2 sensor is inexpensive and often clears the lean code entirely on trucks this age.

For code 71: inspect the vacuum line running to the EGR valve for cracks or collapsed sections, then apply vacuum directly to the valve with a hand pump. It should hold vacuum. If you open it at idle the engine should stumble or stall — that confirms the valve mechanism works. A valve that won’t hold vacuum has failed. Stuck open means rough idle all the time; stuck closed means no driveability impact but the code stays.

Getting clean for smog

Pulling the EFI fuse or briefly disconnecting the battery clears stored codes on the 1989 22RE. But clearing codes without fixing the underlying problems just means they return before the smog test, and in some states the readiness monitors need time to complete a drive cycle before the truck can be tested anyway. Fix the lean condition and the EGR, and the smog situation largely resolves itself. There is no shortcut around the actual repair.