Analog vs Digital O2 Sensors

[sjrobinson]

I’ve looked into this in the past and as I analyze the data from other cars I notice something odd about mine. I’m wondering if its model and make specific or perhaps an underlying issue. I’m always wanting to keep my Accord in good condition.

If the info I read was correct, with the introduction of downstream and upstream sensors in a car, they were made with two different types of data collection: Analog and Digital.

The upstream o2 sensor, collecting data for AFR, is said to send digital signals. The downstream, reading the cat converter efficiency, is analog.

When I analyze different cars using a scan tool I see the spikes (digital) of the upstream sensor and the flat lines (analog) of the downstream sensor. However on my car I see analog data coming from both sensors. My car is a 97 Accord. Is that how the sensors were designed or is there a problem? They are aftermarket sensors, would a downstream sensor placed in the upstream spot cause this?

I’m curious since I would think that a digital signal would provide quicker and more accurate AFR readings for the computer.

Any ideas? I would love to learn more about the nuances in o2 sensor design and behavior.

Thanks

Topic

[Paul]

An ECU is a microcontroller – a minicomputer with inputs from sensors and outputs to relays, actuators, etc. The micrcontroller has firmware, or software permanently stored on the device, which runs over-and-over in a loop that controls various engine parameters. The firmware can be updated, and this is often referred to as “reflashing the PROM”. I had a mid-80’s Buick that had this style of ECU, but it also had a lot of “analog” vacuum lines for controlling the engine.

There is another style of controller known as a PID. I don’t have much experience with these. From what I understand, it’s a set of analog circuits that provides feedback for control, like the emissions system. Basically, the PID balances output signal to an everchanging input signal in order to stabilize the system within predetermined limits. PIDs are commonplace in automated systems, so it wouldn’t surprise me if there is one or more PIDs under the hood.

[Kevin Criswell]

[quote=”Hanneman” post=75947]An ECU is a microcontroller – a minicomputer with inputs from sensors and outputs to relays, actuators, etc. The micrcontroller has firmware, or software permanently stored on the device, which runs over-and-over in a loop that controls various engine parameters. The firmware can be updated, and this is often referred to as “reflashing the PROM”. I had a mid-80’s Buick that had this style of ECU, but it also had a lot of “analog” vacuum lines for controlling the engine.

There is another style of controller known as a PID. I don’t have much experience with these. From what I understand, it’s a set of analog circuits that provides feedback for control, like the emissions system. Basically, the PID balances output signal to an everchanging input signal in order to stabilize the system within predetermined limits. PIDs are commonplace in automated systems, so it wouldn’t surprise me if there is one or more PIDs under the hood.[/quote]

http://en.wikipedia.org/wiki/PID_controller

Got to be careful using the acronym PID. In automotive PID usually refers to Parameter Identification. A PID is coding that can request data from the onboard controller. PIDs are often referenced in mode selection mode $06 allows the tech to read the raw data from monitor and can allow a technician to see if a component will pass or fail and see just how much a component passed or failed.

Mode $06 data is often used when you request “pending failure” codes, these are sensors or circuits that have passed, but barely.

[Author]

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