# Toyota Highlander Hybrid 2006: Codes P0171, P0174, P0037

**URL:** <https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964>\
**Category:** Maintenance/Repairs\
**Tags:** highlanderhybrid, toyota\
**Created:** [July 30, 2018, 5:20pm UTC](https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964 "2018-07-30T17:20:09Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![pecosdiamonds](https://avatars.discourse-cdn.com/v4/letter/p/d78d45/32.png) [@pecosdiamonds](https://community.cartalk.com/u/pecosdiamonds)\
**Post date:** [July 30, 2018, 5:20pm UTC](https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964/1 "2018-07-30T17:20:09Z")

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My Highlander has about 170,000 miles, and recently the P0171, P0174, P0037 codes have come up. I replaced the MAF sensor based on some advice and reset the codes, but the P0037 code returned and I imagine the others will as well.

I was wondering if these 3 codes together indicate some common problem?

P0171: System too lean bank 1  
P0174: System too lean bank 2  
P0037: H02S Heater Control Circuit Low Bank 1 Sensor 2

Thanks,

Evan

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**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\
**Post date:** [July 31, 2018, 12:30am UTC](https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964/2 "2018-07-31T00:30:54Z")

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P0037 the heater circuit for that particular oxygen sensor . . . bank 2 downstream sensor, the one after the cat . . . is probably dead. Translation . . . you need to replace that sensor

As for those lean codes . . . are you sure the maf sensor didn’t take care of the problem?

Do you have a scanner which will show you live data?

If so, what are the short and long term fuel trims for both banks . . . both at idle, under a load, crusing, etc.?

The oxygen sensor code most likely has nothing to do with the other codes

Any obvious vacuum leaks?

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**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\
**Post date:** [July 31, 2018, 1:41am UTC](https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964/3 "2018-07-31T01:41:06Z")

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There should be a spec in the service data for the resistance of the o2 sensor’s heater. That’s the first test I’d make for the p37 code . As posted above, don’t presume the two lean codes will return. Your MAF replacement may well have addressed that problem. Lean on both banks is usually caused by one of these

- MAF needs cleaning or replacement
- Air leak between air cleaner and throttle body, vacuum, intake manifold, or exhaust system
- Fuel pressure problem

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<div class="post-metadata">

**Author:** ![pecosdiamonds](https://avatars.discourse-cdn.com/v4/letter/p/d78d45/32.png) [@pecosdiamonds](https://community.cartalk.com/u/pecosdiamonds)\
**Post date:** [July 31, 2018, 2:56am UTC](https://community.cartalk.com/t/toyota-highlander-hybrid-2006-codes-p0171-p0174-p0037/121964/4 "2018-07-31T02:56:33Z")

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Thanks guys. I will look into this.