# DiagonalOBDII vs AiQuest

DiagonalOBDII and AiQuest both sit at 5.0 stars, but that hides the real split: 100% of AiQuest's written reviews are positive against 0% of DiagonalOBDII's. AiQuest also leads on in-app purchases (none vs 4). On price, rating, ratings volume and update cadence there is nothing between them.

Both are free to download. DiagonalOBDII sells 4 in-app purchases, starting at $12.99 per month. AiQuest asks for nothing beyond the download.

On the App Store both sit at effectively the same score — 5.0 for DiagonalOBDII against 5.0 for AiQuest. Both are backed by a comparable volume of ratings — 1 and 1 respectively. Written reviews are what separate them: 0% of DiagonalOBDII's written reviews are positive against 100% of AiQuest's.

DiagonalOBDII ships an update every 2 weeks, AiQuest every 3 weeks. The most recent releases landed on October 22, 2026 and October 31, 2026 respectively.

## The numbers

| Metric | DiagonalOBDII | AiQuest |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [5.0 (1 ratings)](https://appshunter.io/ios/app/diagonalobdii/id6743419784/reviews) | [5.0 (1 ratings)](https://appshunter.io/ios/app/aiquest/id6762575511/reviews) |
| Number of ratings | 1 | 1 |
| Positive reviews | 0.0% of reviews | **100.0% of reviews** |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 2 weeks** | Every 3 weeks |
| Monetization | Free with in-app purchases | **Free** |
| Size | 21 MB | 31 MB |
| Requires iOS | 18.1 | **18.0** |
| Devices | iPhone | **iPhone, iPad** |
| Age rating | 4+ | 4+ |
| Developer | [Kyle Louderback](https://appshunter.io/developer/1400068218) | [Brahmani Mekala](https://appshunter.io/developer/1894728311) |

## What reviewers say

### DiagonalOBDII

[App page](https://appshunter.io/ios/app/diagonalobdii/id6743419784)

This app helps mechanics perform vehicle drive cycles more efficiently. It provides real-time monitoring of emissions monitors and diagnostic trouble codes (DTCs), offering clear guidance and instant explanations to ensure vehicles pass inspection quickly and accurately.

**Highlights:** Live drive cycle monitoring, Immediate diagnostic trouble code (DTC) identification, Real-time emissions monitor status, Precise drive cycle parameter guidance, Professional, easy-to-navigate dashboard, Instant code explanations

**In-app purchases (4)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Diagonal Premium Monthly | $12.99 | per month |
| Diagonal Premium Trial | $12.99 | per month |
| Shop Owner - Monthly | $17.99 | per month |
| Diagonal Premium Yearly | $99.99 | per year |


### AiQuest

[App page](https://appshunter.io/ios/app/aiquest/id6762575511)

This AI assistant runs entirely on your device, offering powerful LLM capabilities without sending your data to the cloud. Experience fast, private AI interactions powered by local processing.

**Highlights:** On-device AI processing, Privacy-centric design, High-performance LLM integration, Local data storage, Fast response times

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is DiagonalOBDII free?

DiagonalOBDII is free to download, with in-app purchases available.

### Is AiQuest free?

AiQuest is free to download, with no in-app purchases.

### Which has better reviews, DiagonalOBDII or AiQuest?

DiagonalOBDII and AiQuest are both rated 5.0 out of 5 on the App Store, from 1 and 1 ratings respectively.

### Do DiagonalOBDII or AiQuest have ads?

Neither DiagonalOBDII nor AiQuest shows ads.

### Which is updated more often, DiagonalOBDII or AiQuest?

DiagonalOBDII ships an update every 2 weeks, and AiQuest every 3 weeks. Most recently, DiagonalOBDII was updated on October 22, 2026 and AiQuest on October 31, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*